[OpenMP] Temporarily disable failing runtime tests for clang-12

Following tests were disabled for clang-11 after upgrading to
version 5.0 in D82963:

1. openmp/runtime/test/env/kmp_set_dispatch_buf.c
2. openmp/runtime/test/worksharing/for/kmp_set_dispatch_buf.c

They are also failing for clang-12. Thus this temporary disabling
until they are fixed.

Reviewed By: ABataev

Differential Revision: https://reviews.llvm.org/D84241

Author: saiislam

openmp/runtime/test/env/kmp_set_dispatch_buf.c

@@ -9,7 +9,7 @@
 // RUN: env KMP_DISP_NUM_BUFFERS=3 %libomp-run
 // RUN: env KMP_DISP_NUM_BUFFERS=4 %libomp-run
 // RUN: env KMP_DISP_NUM_BUFFERS=7 %libomp-run
-// UNSUPPORTED: clang-11
+// UNSUPPORTED: clang-11, clang-12
 #include <stdio.h>
 #include <omp.h>
 #include <stdlib.h>

openmp/runtime/test/worksharing/for/kmp_set_dispatch_buf.c

@@ -3,7 +3,7 @@
 // RUN: %libomp-run 1 && %libomp-run 2 && %libomp-run 5
 // RUN: %libomp-compile -DMY_SCHEDULE=guided && %libomp-run 7
 // RUN: %libomp-run 1 && %libomp-run 2 && %libomp-run 5
-// UNSUPPORTED: clang-11
+// UNSUPPORTED: clang-11, clang-12
 #include <stdio.h>
 #include <omp.h>
 #include <stdlib.h>