[Clang] Add clang flag --cstdlib (#183254)
Introduce clang flag --cstdlib based on RFC:
https://discourse.llvm.org/t/rfc-add-command-line-option-for-selecting-c-library/87335
This flag accepts a string i.e. the name of the C library that user
wants to use.
Toolchain drivers can handle this flag as per need or ignore it.
