[clang][OpenMP] Improve handling of non-C/C++ directives (#139961)

The PR139793 added handling of the Fortran-only "workshare" directive,
however there are more such directives, e.g. "allocators". Use the
genDirectiveLanguages function to detect non-C/C++ directives instead of
enumerating them.

Author: kparzysz

clang/lib/Parse/ParseOpenMP.cpp

@@ -2613,9 +2613,8 @@ StmtResult Parser::ParseOpenMPDeclarativeOrExecutableDirective(
     Diag(Tok, diag::err_omp_unknown_directive);
     return StmtError();
   }
-  if (DKind == OMPD_workshare) {
-    // "workshare" is an executable, Fortran-only directive. Treat it
-    // as unknown.
+  if (!(getDirectiveLanguages(DKind) & SourceLanguage::C)) {
+    // Treat directives that are not allowed in C/C++ as unknown.
     DKind = OMPD_unknown;
   }
 

clang/test/OpenMP/openmp_non_c_directives.c

@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -verify -fopenmp -ferror-limit 100 -o - %s
+
+// Test the reaction to some Fortran-only directives.
+
+void foo() {
+#pragma omp allocators // expected-error {{expected an OpenMP directive}}
+#pragma omp do // expected-error {{expected an OpenMP directive}}
+#pragma omp end workshare // expected-error {{expected an OpenMP directive}}
+#pragma omp parallel workshare // expected-warning {{extra tokens at the end of '#pragma omp parallel' are ignored}}
+#pragma omp workshare // expected-error {{expected an OpenMP directive}}
+}
+