[OPENMP] Check that allocated variables are used in private clauses.

According to OpenMP 5.0 standard, 2.11.4 allocate Clause, Restrictions,
For any list item that is specified in the allocate clause on a
directive, a data-sharing attribute clause that may create a private
copy of that list item must be specified on the same directive. Patch
adds the checks for this restriction.

llvm-svn: 357390

Author: alexey-bataev

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -9161,6 +9161,8 @@ def err_expected_allocator_clause : Error<"expected an 'allocator' clause "
 def warn_omp_allocate_thread_on_task_target_directive : Warning<
   "allocator with the 'thread' trait access has unspecified behavior on '%0' directive">,
   InGroup<OpenMPClauses>;
+def err_omp_expected_private_copy_for_allocate : Error<
+  "the referenced item is not found in any private clause on the same directive">;
 } // end of OpenMP category
 
 let CategoryName = "Related Result Type Issue" in {