[OpenMP 5.0] Parsing/sema support for "omp declare mapper" directive.

This patch implements parsing and sema for "omp declare mapper"
directive. User defined mapper, i.e., declare mapper directive, is a new
feature in OpenMP 5.0. It is introduced to extend existing map clauses
for the purpose of simplifying the copy of complex data structures
between host and device (i.e., deep copy). An example is shown below:

    struct S {  int len;  int *d; };
    #pragma omp declare mapper(struct S s) map(s, s.d[0:s.len]) // Memory region that d points to is also mapped using this mapper.

Contributed-by: Lingda Li <lildmh@gmail.com>

Differential Revision: https://reviews.llvm.org/D56326

llvm-svn: 352906
diff --git a/clang/lib/Basic/OpenMPKinds.cpp b/clang/lib/Basic/OpenMPKinds.cpp
index c421517..ea8a46b 100644
--- a/clang/lib/Basic/OpenMPKinds.cpp
+++ b/clang/lib/Basic/OpenMPKinds.cpp
@@ -766,6 +766,16 @@
       break;
     }
     break;
+  case OMPD_declare_mapper:
+    switch (CKind) {
+#define OPENMP_DECLARE_MAPPER_CLAUSE(Name)                                     \
+  case OMPC_##Name:                                                            \
+    return true;
+#include "clang/Basic/OpenMPKinds.def"
+    default:
+      break;
+    }
+    break;
   case OMPD_declare_target:
   case OMPD_end_declare_target:
   case OMPD_unknown:
@@ -1000,6 +1010,7 @@
   case OMPD_cancel:
   case OMPD_flush:
   case OMPD_declare_reduction:
+  case OMPD_declare_mapper:
   case OMPD_declare_simd:
   case OMPD_declare_target:
   case OMPD_end_declare_target: