[OpenMP] Handle function declaration or definition omp pragmas in C mode

[rpenacob]

Summary

Clang crashes when a C++ like struct with a declare variant or declare simd pragma is parsed in C mode. Skip the pragma in this situation and leave the parser emit a diagnostic.

clang/lib/Parse/ParseOpenMP.cpp

if (Actions.isInOpenMPDeclareVariantScope())
       Actions.ActOnOpenMPEndDeclareVariant();
     else
       Diag(Loc, diag::err_expected_begin_declare_variant);
     ConsumeToken();
     break;
   }
   case OMPD_declare_variant:
   case OMPD_declare_simd: {
+    // Only allowed in C++ mode
+    if (!getLangOpts().CPlusPlus && getCurScope()->isClassScope())
+      break;
     // The syntax is:
     // { #pragma omp declare {simd|variant} }
     // <function-declaration-or-definition>
     //
     CachedTokens Toks;
     Toks.push_back(Tok);
     ConsumeToken();
     while (Tok.isNot(tok::annot_pragma_openmp_end)) {

clang/test/OpenMP/declare_simd_messages.c

+// RUN: %clang_cc1 -triple=x86_64-pc-win32 -verify -fopenmp -x c -fms-extensions -Wno-pragma-pack %s
+
+struct S0 {
+  // expected-error@+2 {{field 'foo' declared as a function}}
+  #pragma omp declare simd
+  void foo();
+};
+
+struct S1 {
+  // expected-error@+3 {{field 'bar' declared as a function}}
+  // expected-error@+2 {{expected ';' at end of declaration list}}
+  #pragma omp declare simd
+  void bar() {}
+};

clang/test/OpenMP/declare_variant_messages.c

 int conflicting_nested_score(void);
 #pragma omp end declare variant
 
 // FIXME: We should build the conjuction of different conditions, see also the score fixme above.
 #pragma omp begin declare variant match(user = {condition(1)})
 #pragma omp declare variant(foo) match(user = {condition(1)}) // expected-error {{nested user conditions in OpenMP context selector not supported (yet)}}
 int conflicting_nested_condition(void);
 #pragma omp end declare variant
+
+struct S0 {
+  // expected-error@+2 {{field 'foo' declared as a function}}
+  #pragma omp declare variant
+  void foo();
+};
+
+struct S1 {
+  // expected-error@+3 {{field 'bar' declared as a function}}
+  // expected-error@+2 {{expected ';' at end of declaration list}}
+  #pragma omp declare variant
+  void bar() {}
+};