[OpenMP] Disable tests that are not supported by GCC if it is used for testing

[tianshilei1992]

Summary

GCC doesn't support -fopenmp-version, causing test failure if the compiler used
for testing is GCC.

GCC's OpenMP 5.2 support is very limited yet. Disable those tests requiring 5.2
feature for GCC as well.

We might want to take a look at all libomp tests and mark those tests that
don't support GCC yet.

[tianshilei1992]

add one more

[tianshilei1992]

ping

[ABataev]

LG

openmp/runtime/test/atomic/omp-atomic-compare-signedness.c

 // Check that omp atomic compare handles signedness of integer comparisons
 // correctly.
 //
 // At one time, a bug sometimes reversed the signedness.
 
 // RUN: %libomp-compile -fopenmp-version=51
 // RUN: %libomp-run | FileCheck %s
 
+// This test uses -fopenmp-version, which is not a compiler flag that GCC
+// supports.
+// UNSUPPORTED: gcc
+
 // High parallelism increases our chances of detecting a lack of atomicity.
 #define NUM_THREADS_TRY 256
 
 #include <limits.h>
 #include <omp.h>
 #include <stdio.h>
 
 int main() {

openmp/runtime/test/teams/teams-atomic.c

 // Check that omp atomic is permitted and behaves when strictly nested within
 // omp teams.  This is an extension to OpenMP 5.2 and is enabled by default.
 
 // RUN: %libomp-compile-and-run | FileCheck %s
+// GCC has really limited OpenMP 5.2 support yet.
+// UNSUPPORTED: gcc
 
 #include <omp.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <string.h>
 
 // High parallelism increases our chances of detecting a lack of atomicity.
 #define NUM_TEAMS_TRY 256