[clang] [Clang] Add 'CLANG_ALLOW_IMPLICIT_RPATH' to enable toolchain use of -rpath (PR #82004)

[Tom Stellard via cfe-commits]

tstellar wrote:

Could we have the upstream default be to install a clang.cfg file in bin/ which has -fimplicit-openmp-rpath (or whatever the hoption is)?  

https://github.com/llvm/llvm-project/pull/82004