[OPENMP50]Initial support for scan directive.

Addedi basic parsing/sema/serialization support for scan directive.
diff --git a/clang/lib/Sema/SemaExceptionSpec.cpp b/clang/lib/Sema/SemaExceptionSpec.cpp
index 5c9844e..6eb5b71 100644
--- a/clang/lib/Sema/SemaExceptionSpec.cpp
+++ b/clang/lib/Sema/SemaExceptionSpec.cpp
@@ -1439,6 +1439,7 @@
   case Stmt::OMPDistributeSimdDirectiveClass:
   case Stmt::OMPFlushDirectiveClass:
   case Stmt::OMPDepobjDirectiveClass:
+  case Stmt::OMPScanDirectiveClass:
   case Stmt::OMPForDirectiveClass:
   case Stmt::OMPForSimdDirectiveClass:
   case Stmt::OMPMasterDirectiveClass: