[CIR] Add handlers for 'using enum' and namespace alias

These decl types don't require any code generation, though when debug info
is implemented, we will need to add handling for that. Until then, we
just need to have a handler  so they don't generate an NYI error.

Author: andykaylor

clang/lib/CIR/CodeGen/CIRGenModule.cpp

@@ -1258,6 +1258,8 @@ void CIRGenModule::emitTopLevelDecl(Decl *decl) {
   case Decl::Enum:
   case Decl::Using:          // using X; [C++]
   case Decl::UsingDirective: // using namespace X; [C++]
+  case Decl::UsingEnum:      // using enum X; [C++]
+  case Decl::NamespaceAlias:
   case Decl::Typedef:
   case Decl::TypeAlias: // using foo = bar; [C++11]
   case Decl::Record:

clang/test/CIR/CodeGen/enum.cpp

@@ -14,3 +14,14 @@ int f() {
 
 // CHECK: cir.func{{.*}} @_Z1fv
 // CHECK:    cir.const #cir.int<1> : !u32i
+
+namespace test {
+  using enum Numbers;
+};
+
+int f2() {
+  return test::Two;
+}
+
+// CHECK: cir.func{{.*}} @_Z2f2v
+// CHECK:    cir.const #cir.int<2> : !u32i

clang/test/CIR/CodeGen/namespace.cpp

@@ -93,3 +93,11 @@ void f7() {
 }
 
 // CHECK: cir.func{{.*}} @_Z2f7v()
+
+namespace test_alias = test;
+
+int f8() {
+  return test_alias::g2;
+}
+
+// CHECK: cir.func{{.*}} @_Z2f8v()