[OPENMP50]Initial support for scan directive.

Addedi basic parsing/sema/serialization support for scan directive.
diff --git a/clang/lib/Parse/ParseOpenMP.cpp b/clang/lib/Parse/ParseOpenMP.cpp
index 6f6de47..c5026f7 100644
--- a/clang/lib/Parse/ParseOpenMP.cpp
+++ b/clang/lib/Parse/ParseOpenMP.cpp
@@ -1843,6 +1843,7 @@
   case OMPD_taskgroup:
   case OMPD_flush:
   case OMPD_depobj:
+  case OMPD_scan:
   case OMPD_for:
   case OMPD_for_simd:
   case OMPD_sections:
@@ -2066,6 +2067,7 @@
   }
   case OMPD_flush:
   case OMPD_depobj:
+  case OMPD_scan:
   case OMPD_taskyield:
   case OMPD_barrier:
   case OMPD_taskwait: