NFC: fixed typo #ifdef --> #if to allow macro set to 0 work correctly

git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@365642 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/runtime/src/kmp.h b/runtime/src/kmp.h
index 38a16d1..3db2754 100644
--- a/runtime/src/kmp.h
+++ b/runtime/src/kmp.h
@@ -3663,7 +3663,7 @@
 extern void __kmp_finish_implicit_task(kmp_info_t *this_thr);
 extern void __kmp_free_implicit_task(kmp_info_t *this_thr);
 
-#ifdef OMP_50_ENABLED
+#if OMP_50_ENABLED
 extern kmp_event_t *__kmpc_task_allow_completion_event(ident_t *loc_ref,
                                                        int gtid,
                                                        kmp_task_t *task);