[OpenMP] Remove -Wno-enum-constexpr-conversion (#81318)

This effectively reverts commit
9ff0cc7. For some reason "git revert"
lead to "no changes" after fixing conflicts, so a clean revert was not
possible.

The original issue (#57022) is no longer reproducible even with this
patch, so we can remove the suppression.

This is in line with our goal to make -Wenum-constexpr-conversion a
non-downgradeable error, see #59036.

Co-authored-by: Carlos Gálvez <carlos.galvez@zenseact.com>

Author: carlosgalvezp

openmp/cmake/HandleOpenMPOptions.cmake

@@ -41,7 +41,6 @@ append_if(OPENMP_HAVE_WSIGN_COMPARE_FLAG "-Wsign-compare" CMAKE_C_FLAGS CMAKE_CX
 # printed. Therefore, check for whether the compiler supports options in the
 # form -W<foo>, and if supported, add the corresponding -Wno-<foo> option.
 
-append_if(OPENMP_HAVE_WENUM_CONSTEXPR_CONVERSION_FLAG "-Wno-enum-constexpr-conversion" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 append_if(OPENMP_HAVE_WEXTRA_FLAG "-Wno-extra" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 append_if(OPENMP_HAVE_WPEDANTIC_FLAG "-Wno-pedantic" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 append_if(OPENMP_HAVE_WMAYBE_UNINITIALIZED_FLAG "-Wno-maybe-uninitialized" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)

openmp/cmake/config-ix.cmake

@@ -33,7 +33,6 @@ check_cxx_compiler_flag(-Wsign-compare OPENMP_HAVE_WSIGN_COMPARE_FLAG)
 # printed. Therefore, check for whether the compiler supports options in the
 # form -W<foo>, and if supported, add the corresponding -Wno-<foo> option.
 
-check_cxx_compiler_flag(-Wenum-constexpr-conversion OPENMP_HAVE_WENUM_CONSTEXPR_CONVERSION_FLAG)
 check_cxx_compiler_flag(-Wextra OPENMP_HAVE_WEXTRA_FLAG)
 check_cxx_compiler_flag(-Wpedantic OPENMP_HAVE_WPEDANTIC_FLAG)
 check_cxx_compiler_flag(-Wmaybe-uninitialized OPENMP_HAVE_WMAYBE_UNINITIALIZED_FLAG)