[OpenMP51] Initial support for masked directive and filter clause

Adds basic parsing/sema/serialization support for the #pragma omp masked
directive.

Reviewed By: ABataev

Differential Revision: https://reviews.llvm.org/D99995

GitOrigin-RevId: 1a43fd27691c6ae5c3d725ca7c6f4fd19357f4b8
diff --git a/lib/Semantics/check-omp-structure.cpp b/lib/Semantics/check-omp-structure.cpp
index ec872d2..dcb7001 100644
--- a/lib/Semantics/check-omp-structure.cpp
+++ b/lib/Semantics/check-omp-structure.cpp
@@ -772,6 +772,7 @@
 CHECK_SIMPLE_CLAUSE(Use, OMPC_use)
 CHECK_SIMPLE_CLAUSE(Novariants, OMPC_novariants)
 CHECK_SIMPLE_CLAUSE(Nocontext, OMPC_nocontext)
+CHECK_SIMPLE_CLAUSE(Filter, OMPC_filter)
 
 CHECK_REQ_SCALAR_INT_CLAUSE(Allocator, OMPC_allocator)
 CHECK_REQ_SCALAR_INT_CLAUSE(Grainsize, OMPC_grainsize)