This is Kubuntu 14.04.5 LTS / x86_64 with gcc 4.8.4 (so, running KDE desktop, if that matters) here.
I tried your newest Ubuntu 14 gcc4.8 binary release and it crashes as soon as I try to create a TCanvas or a TBrowser:
[...] $ which root
/opt/ROOT/releases/root_v6.10.06/bin/root
[...] $ root -l
root [0] new TCanvas
*** Break *** illegal instruction
===========================================================
There was a crash.
This is the entire stack trace of all threads:
===========================================================
#0 0x00007fdfa71c095c in __libc_waitpid (pid=6691, stat_loc=stat_loc
entry=0x7ffd3fcea340, options=options
entry=0) at ../sysdeps/unix/sysv/linux/waitpid.c:31
#1 0x00007fdfa7142232 in do_system (line=<optimized out>) at ../sysdeps/posix/system.c:148
#2 0x00007fdfa7cb3789 in TUnixSystem::StackTrace() () from /opt/ROOT/releases/root_v6.10.06/lib/libCore.so
#3 0x00007fdfa7cb5fbc in TUnixSystem::DispatchSignals(ESignals) () from /opt/ROOT/releases/root_v6.10.06/lib/libCore.so
#4 <signal handler called>
#5 0x00007fdfa338a283 in (anonymous namespace)::SimplifyCFGOpt::SimplifySwitch(llvm::SwitchInst*, llvm::IRBuilder<llvm::ConstantFolder, llvm::IRBuilderDefaultInserter>&) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#6 0x00007fdfa421d207 in llvm::SimplifyCFG(llvm::BasicBlock*, llvm::TargetTransformInfo const&, unsigned int, llvm::AssumptionCache*, llvm::SmallPtrSetImpl<llvm::BasicBlock*>*) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#7 0x00007fdfa40fe009 in iterativelySimplifyCFG(llvm::Function&, llvm::TargetTransformInfo const&, llvm::AssumptionCache*, unsigned int) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#8 0x00007fdfa40fe5d1 in simplifyFunctionCFG(llvm::Function&, llvm::TargetTransformInfo const&, llvm::AssumptionCache*, int) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#9 0x00007fdfa4cef056 in llvm::FPPassManager::runOnFunction(llvm::Function&) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#10 0x00007fdfa4cef41b in llvm::FPPassManager::runOnModule(llvm::Module&) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#11 0x00007fdfa4cef6f0 in llvm::legacy::PassManagerImpl::run(llvm::Module&) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#12 0x00007fdfa350e94f in cling::Interpreter::addModule(llvm::Module*, int) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#13 0x00007fdfa356226b in cling::IncrementalParser::codeGenTransaction(cling::Transaction*) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#14 0x00007fdfa3561e40 in cling::IncrementalParser::commitTransaction(llvm::PointerIntPair<cling::Transaction*, 2u, cling::IncrementalParser::EParseResult, llvm::PointerLikeTypeTraits<cling::Transaction*>, llvm::PointerIntPairInfo<cling::Transaction*, 2u, llvm::PointerLikeTypeTraits<cling::Transaction*> > >&, bool) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#15 0x00007fdfa3565a35 in cling::IncrementalParser::Compile(llvm::StringRef, cling::CompilationOptions const&) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#16 0x00007fdfa350bd5c in cling::Interpreter::DeclareInternal(std::string const&, cling::CompilationOptions const&, cling::Transaction**) const () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#17 0x00007fdfa350be9e in cling::Interpreter::declare(std::string const&, cling::Transaction**) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#18 0x00007fdfa350c430 in cling::Interpreter::DeclareCFunction(llvm::StringRef, llvm::StringRef, bool) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#19 0x00007fdfa350da65 in cling::Interpreter::compileFunction(llvm::StringRef, llvm::StringRef, bool, bool) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#20 0x00007fdfa34ce8f6 in TClingCallFunc::compile_wrapper(std::string const&, std::string const&, bool) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#21 0x00007fdfa34d1d30 in TClingCallFunc::make_wrapper() () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#22 0x00007fdfa34d620a in TClingCallFunc::IFacePtr() () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#23 0x00007fdfa34d62a3 in TClingCallFunc::ExecInt(void*) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#24 0x00007fdfa7c88fe0 in TMethodCall::Execute(void*, long&) () from /opt/ROOT/releases/root_v6.10.06/lib/libCore.so
#25 0x00007fdfa7ba419b in TApplication::LoadGraphicsLibs() () from /opt/ROOT/releases/root_v6.10.06/lib/libCore.so
#26 0x00007fdfa7ba367a in TApplication::InitializeGraphics() () from /opt/ROOT/releases/root_v6.10.06/lib/libCore.so
#27 0x00007fdf9d301b22 in TCanvas::Init() () from /opt/ROOT/releases/root_v6.10.06/lib/libGpad.so
#28 0x00007fdf9d3034f3 in TCanvas::Constructor(char const*, char const*, int) () from /opt/ROOT/releases/root_v6.10.06/lib/libGpad.so
#29 0x00007fdf9d3055ce in TCanvas::TCanvas(bool) () from /opt/ROOT/releases/root_v6.10.06/lib/libGpad.so
#30 0x00007fdfa8429052 in ?? ()
#31 0x0000000000000000 in ?? ()
===========================================================
The lines below might hint at the cause of the crash.
You may get help by asking at the ROOT forum http://root.cern.ch/forum.
Only if you are really convinced it is a bug in ROOT then please submit a
report at http://root.cern.ch/bugs. Please post the ENTIRE stack trace
from above as an attachment in addition to anything else
that might help us fixing this issue.
===========================================================
#5 0x00007fdfa338a283 in (anonymous namespace)::SimplifyCFGOpt::SimplifySwitch(llvm::SwitchInst*, llvm::IRBuilder<llvm::ConstantFolder, llvm::IRBuilderDefaultInserter>&) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#6 0x00007fdfa421d207 in llvm::SimplifyCFG(llvm::BasicBlock*, llvm::TargetTransformInfo const&, unsigned int, llvm::AssumptionCache*, llvm::SmallPtrSetImpl<llvm::BasicBlock*>*) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#7 0x00007fdfa40fe009 in iterativelySimplifyCFG(llvm::Function&, llvm::TargetTransformInfo const&, llvm::AssumptionCache*, unsigned int) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#8 0x00007fdfa40fe5d1 in simplifyFunctionCFG(llvm::Function&, llvm::TargetTransformInfo const&, llvm::AssumptionCache*, int) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#9 0x00007fdfa4cef056 in llvm::FPPassManager::runOnFunction(llvm::Function&) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#10 0x00007fdfa4cef41b in llvm::FPPassManager::runOnModule(llvm::Module&) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#11 0x00007fdfa4cef6f0 in llvm::legacy::PassManagerImpl::run(llvm::Module&) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#12 0x00007fdfa350e94f in cling::Interpreter::addModule(llvm::Module*, int) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#13 0x00007fdfa356226b in cling::IncrementalParser::codeGenTransaction(cling::Transaction*) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#14 0x00007fdfa3561e40 in cling::IncrementalParser::commitTransaction(llvm::PointerIntPair<cling::Transaction*, 2u, cling::IncrementalParser::EParseResult, llvm::PointerLikeTypeTraits<cling::Transaction*>, llvm::PointerIntPairInfo<cling::Transaction*, 2u, llvm::PointerLikeTypeTraits<cling::Transaction*> > >&, bool) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#15 0x00007fdfa3565a35 in cling::IncrementalParser::Compile(llvm::StringRef, cling::CompilationOptions const&) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#16 0x00007fdfa350bd5c in cling::Interpreter::DeclareInternal(std::string const&, cling::CompilationOptions const&, cling::Transaction**) const () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#17 0x00007fdfa350be9e in cling::Interpreter::declare(std::string const&, cling::Transaction**) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#18 0x00007fdfa350c430 in cling::Interpreter::DeclareCFunction(llvm::StringRef, llvm::StringRef, bool) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#19 0x00007fdfa350da65 in cling::Interpreter::compileFunction(llvm::StringRef, llvm::StringRef, bool, bool) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#20 0x00007fdfa34ce8f6 in TClingCallFunc::compile_wrapper(std::string const&, std::string const&, bool) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#21 0x00007fdfa34d1d30 in TClingCallFunc::make_wrapper() () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#22 0x00007fdfa34d620a in TClingCallFunc::IFacePtr() () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#23 0x00007fdfa34d62a3 in TClingCallFunc::ExecInt(void*) () from /opt/ROOT/releases/root_v6.10.06/lib/libCling.so
#24 0x00007fdfa7c88fe0 in TMethodCall::Execute(void*, long&) () from /opt/ROOT/releases/root_v6.10.06/lib/libCore.so
#25 0x00007fdfa7ba419b in TApplication::LoadGraphicsLibs() () from /opt/ROOT/releases/root_v6.10.06/lib/libCore.so
#26 0x00007fdfa7ba367a in TApplication::InitializeGraphics() () from /opt/ROOT/releases/root_v6.10.06/lib/libCore.so
#27 0x00007fdf9d301b22 in TCanvas::Init() () from /opt/ROOT/releases/root_v6.10.06/lib/libGpad.so
#28 0x00007fdf9d3034f3 in TCanvas::Constructor(char const*, char const*, int) () from /opt/ROOT/releases/root_v6.10.06/lib/libGpad.so
#29 0x00007fdf9d3055ce in TCanvas::TCanvas(bool) () from /opt/ROOT/releases/root_v6.10.06/lib/libGpad.so
#30 0x00007fdfa8429052 in ?? ()
#31 0x0000000000000000 in ?? ()
===========================================================
Root >