[OpenMP] Add ATTACH map-type to OMPConstants.h, to align with omptarget.h. (#161791)

The clang changes that use this map-type are in #153683.

Author: abhinavgaba

llvm/include/llvm/Frontend/OpenMP/OMPConstants.h

@@ -239,6 +239,9 @@ enum class OpenMPOffloadMappingFlags : uint64_t {
   // dynamic.
   // This is an OpenMP extension for the sake of OpenACC support.
   OMP_MAP_OMPX_HOLD = 0x2000,
+  // Attach pointer and pointee, after processing all other maps.
+  // Applicable to map-entering directives. Does not change ref-count.
+  OMP_MAP_ATTACH = 0x4000,
   /// Signal that the runtime library should use args as an array of
   /// descriptor_dim pointers and use args_size as dims. Used when we have
   /// non-contiguous list items in target update directive