[DebugInfo] Fix the mismatching between C++ language tags and Dwarf versions.

Summary: The tags DW_LANG_C_plus_plus_14 and DW_LANG_C_plus_plus_11, introduced in Dwarf-5, are unexpected in previous versions. Fixing the mismathing doesn't have any drawbacks for any other debuggers, but helps dbx.

Reviewed By: aprantl, shchenz

Differential Revision: https://reviews.llvm.org/D99250