[Clang] Add helper method to determine if a nonvirtual base has an entry in the LLVM struct

This patch adds a helper method to determine if a nonvirtual base has an entry in the LLVM struct. Such a base may not have an entry
if the base does not have any fields/bases itself that would change the size of the struct. This utility method is useful for other frontends (Polygeist) that use Clang as an API to generate code.

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D122502

clang/lib/CodeGen/CGRecordLayout.h

@@ -200,6 +200,12 @@ public:
     return FieldInfo.lookup(FD);
   }
 
+  // Return whether the following non virtual base has a corresponding
+  // entry in the LLVM struct.
+  bool hasNonVirtualBaseLLVMField(const CXXRecordDecl *RD) const {
+    return NonVirtualBases.count(RD);
+  }
+
   unsigned getNonVirtualBaseLLVMFieldNo(const CXXRecordDecl *RD) const {
     assert(NonVirtualBases.count(RD) && "Invalid non-virtual base!");
     return NonVirtualBases.lookup(RD);