With the standalone and project builds removed,
`OPENMP_TEST_COMPILER_HAS_OMP_H`/`config.test_compiler_has_omp_h` is set
to constant 1, which causes the `config.omp_header_directory` search
path NOT to be added to `%flags-use-compiler-omp-h`, causing the system
`omp.h` used, or the only test actually using it
(`omp50_taskdep_depobj.c`) failing if that one is not available.
The intention of `OPENMP_TEST_COMPILER_HAS_OMP_H` was to use gcc's
`omp.h` which declares `omp_depend_t` differently than our `omp.h`
(https://reviews.llvm.org/D108790). Using `OPENMP_TEST_C_COMPILER=gcc`
was used to test libomp's GOMP compatibility layer, but testing it is
currently unmaintained and has no buildbot (60 failing tests out of 389
with gcc-13, not including OMPD and OMPT). If updating testing for GOMP,
then gcc's own `omp.h` must be used for all tests: using the GOMP ABI
requires using GOMP's `omp.h`.
Closes: #187879
8ab7b37e74