These have the same purposes but two different implementations. llvm_check_compiler_linker_flag uses CMAKE_REQUIRED_FLAGS which affects flags used both for compilation and linking which is problematic because some flags may be link-only and trigger unused argument warning when set during compilation. llvm_check_linker_flag does not have this issue so we chose it as the prevailaing implementation. Differential Revision: https://reviews.llvm.org/D143052