[OpenMP] Replace libomp_check_linker_flag with llvm_check_compiler_linker_flag

Replace the custom libomp_check_linker_flag() implementation with
llvm_check_compiler_linker_flag() from the common cmake utils. Due
to the way the custom implementation is implemented (capturing
output from an entire nested cmake invocation) it can easily end
up incorrectly detecting flags as unavailable, e.g. because "error",
"unknown" or similar occurs inside compiler flags, the directory
name, etc.

Fixes https://github.com/llvm/llvm-project/issues/62240.

Differential Revision: https://reviews.llvm.org/D148798