add AST test

Author: Keenuts

clang/test/AST/HLSL/vk.pushconstant.hlsl

@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -triple spirv-unknown-vulkan1.3-compute -x hlsl -ast-dump -o - %s | FileCheck %s
+
+struct S {
+  int value;
+};
+
+[[vk::push_constant]] S PC;
+// CHECK:      VarDecl 0x[[A:[0-9a-f]+]] <line:7:23, col:25> col:25 PC 'hlsl_push_constant S'
+// CHECK-NEXT: HLSLVkPushConstantAttr 0x[[A:[0-9a-f]+]] <col:3, col:7>
+
+[numthreads(1, 1, 1)]
+void main() { }