[OpenMP] Fix crash on invalid with cancel directive

If the next token after 'cancel' is a special token, we would trigger
an assertion. We should be consuming any token, same as elsewhere in
the function.

Note, we could check for an unknown directive and do different error
recovery, but that caused too many behavioral changes for other tests
in the form of "unexpected tokens ignored" diagnostics that didn't seem
like an improvement for the test cases.

Fixes #139360

Author: AaronBallman

clang/docs/ReleaseNotes.rst

@@ -922,6 +922,7 @@ OpenMP Support
   an invalid expression. (#GH139073)
 - Fixed a crashing bug with ``omp simd collapse`` if the argument to
   ``collapse`` was an invalid expression. (#GH138493)
+- Fixed a crashing bug with a malformed ``cancel`` directive. (#GH139360)
 - Fixed a crashing bug with ``omp distribute dist_schedule`` if the argument to
   ``dist_schedule`` was not strictly positive. (#GH139266)
 

clang/lib/Parse/ParseOpenMP.cpp

@@ -2487,7 +2487,7 @@ StmtResult Parser::ParseOpenMPExecutableDirective(
   } else if (DKind == OMPD_cancellation_point || DKind == OMPD_cancel) {
     CancelRegion = parseOpenMPDirectiveKind(*this);
     if (Tok.isNot(tok::annot_pragma_openmp_end))
-      ConsumeToken();
+      ConsumeAnyToken();
   }
 
   if (isOpenMPLoopDirective(DKind))

clang/test/OpenMP/cancel_messages.cpp

@@ -93,3 +93,8 @@ label1 : {
   return 0;
 }
 
+namespace GH139360 {
+void f(){
+#pragma omp cancel( // expected-error {{one of 'for', 'parallel', 'sections' or 'taskgroup' is expected}}
+}
+} // namesapce GH139360