[openmp] Only try to add the -mrtm flag on i386/x86_64

[mstorsjo]

Summary

Clang does accept the flag for any architecture, but prints a
warning:

clang-16: warning: argument unused during compilation: '-mrtm' [-Wunused-command-line-argument]

This flag is documented as an x86 specific flag, so don't try to
add it for other architectures, to silence this warning.

[Meinersbur]

LGTM

openmp/runtime/cmake/LibompHandleFlags.cmake

function(libomp_get_cxxflags cxxflags)
   libomp_append(flags_local -Wno-uninitialized LIBOMP_HAVE_WNO_UNINITIALIZED_FLAG)
   libomp_append(flags_local -Wno-return-type-c-linkage LIBOMP_HAVE_WNO_RETURN_TYPE_C_LINKAGE_FLAG)
   libomp_append(flags_local -Wno-cast-qual LIBOMP_HAVE_WNO_CAST_QUAL_FLAG)
   libomp_append(flags_local -Wno-int-to-void-pointer-cast LIBOMP_HAVE_WNO_INT_TO_VOID_POINTER_CAST_FLAG)
   # libomp_append(flags_local -Wconversion LIBOMP_HAVE_WCONVERSION_FLAG)
   libomp_append(flags_local /GS LIBOMP_HAVE_GS_FLAG)
   libomp_append(flags_local /EHsc LIBOMP_HAVE_EHSC_FLAG)
   libomp_append(flags_local /Oy- LIBOMP_HAVE_OY__FLAG)
+  if(${IA32} OR ${INTEL64})
     libomp_append(flags_local -mrtm LIBOMP_HAVE_MRTM_FLAG)
+  endif()
   # Intel(R) C Compiler flags
   libomp_append(flags_local /Qsafeseh LIBOMP_HAVE_QSAFESEH_FLAG)
   libomp_append(flags_local -Qoption,cpp,--extended_float_types LIBOMP_HAVE_EXTENDED_FLOAT_TYPES_FLAG)
   libomp_append(flags_local -Qlong_double LIBOMP_HAVE_LONG_DOUBLE_FLAG)
   libomp_append(flags_local -Qdiag-disable:177 LIBOMP_HAVE_DIAG_DISABLE_177_FLAG)
   if(${RELEASE_BUILD} OR ${RELWITHDEBINFO_BUILD})
     libomp_append(flags_local -Qinline-min-size=1 LIBOMP_HAVE_INLINE_MIN_SIZE_FLAG)
   endif()