Readd: Do not instantiate template ctors to make it take an ioctortype arg.

Fixes ROOT-5547.

Reverting it is too rash.  It introduce a backward incompatiblity
but the feature is less important that fixing the bug introduced
by its incorrect implementation.
Reimplement GetUserHomeDirectory().
Update header name.
Update header name.
Options moved to llvm; CI->createDiagnostics; Path
Revert clang::Decl::ClearLinkageCache() patch; implement here instead.
Non-MC JIT does not support exception handling anymore.
Options moved from clang to llvm.
Header renamed.
Use StringRef instead of Path.
Use StringRef instead of Path.
File magic moved / changed.
Fix include.
Rmove invalud / unused fwd decl of Path.
Fix small string / $HOME mess.
New DeduceAutoType() interface.
Remove more Paths.
Updated signature.
Header renamed.
Fix hack.