[OMPT] Make sure that OMPT is enabled when accessing internals of the runtime

The three switch fallthrough generate a warning with -Wimplicit-fallthrough.
Two are documented as fallthrough, one is not, but I think the intention is to also fallthrough in kmp_tasking.cpp.

Not sure whether kmp.h is the best place to define the macro.

Reviewers: jlpeyton, AndreyChurbanov, Hahnfeld

Reviewed By: jlpeyton

Tags: #openmp

Differential Revision: https://reviews.llvm.org/D56397

llvm-svn: 353052
diff --git a/openmp/runtime/src/kmp_runtime.cpp b/openmp/runtime/src/kmp_runtime.cpp
index 724f231..e7b50ff 100644
--- a/openmp/runtime/src/kmp_runtime.cpp
+++ b/openmp/runtime/src/kmp_runtime.cpp
@@ -6421,6 +6421,7 @@
         // library. Assume the other library is alive.
         // WARN( ... ); // TODO: Issue a warning.
         file_name = "unknown library";
+        KMP_FALLTHROUGH();
       // Attention! Falling to the next case. That's intentional.
       case 1: { // Neighbor is alive.
         // Check it is allowed.