Is there any way to tell ACLiC to use other than
hard wired CXX compiler using either environment
variable or rootrc resource variable? I know that
I may be able to use TSystem::SetMakeSharedLib()
directly. But if I can replace just compiler name (e.g. from
g++ to my own my-g++ …) it will be helpful?
Usually (and you can check by look a gSystem->GetMakeSharedLib()), the compiler is requested with an explicit path. Hence you should be able to select the compiler you want (assuming the name is still g++) by changing the PATH environment variable.
Otherwise you need to call Get/SetMakeSharedLib (which you could do in a rootlogon.C file).