[X86] Add -fexperimental-new-constant-interpreter test coverage to the BSWAP constexpr test files (llvm#156061)

Update tests to use builtin_test_helpers.h and the TEST_CONSTEXPR helper macro

Partial fix for llvm#155814

Author: RKSimon

clang/test/CodeGen/X86/x86-bswap.c

@@ -1,45 +1,41 @@
 // RUN: %clang_cc1 -x c -ffreestanding %s -triple=x86_64-apple-darwin -no-enable-noundef-analysis -emit-llvm -o - | FileCheck %s
 // RUN: %clang_cc1 -x c++ -std=c++11 -ffreestanding %s -triple=x86_64-apple-darwin -no-enable-noundef-analysis -emit-llvm -o - | FileCheck %s
 
+// RUN: %clang_cc1 -x c -ffreestanding %s -triple=x86_64-apple-darwin -no-enable-noundef-analysis -emit-llvm -o - -fexperimental-new-constant-interpreter | FileCheck %s
+// RUN: %clang_cc1 -x c++ -std=c++11 -ffreestanding %s -triple=x86_64-apple-darwin -no-enable-noundef-analysis -emit-llvm -o - -fexperimental-new-constant-interpreter | FileCheck %s
+
+
 #include <x86intrin.h>
+#include "builtin_test_helpers.h"
 
 int test__bswapd(int X) {
 // CHECK-LABEL: test__bswapd
 // CHECK: call i32 @llvm.bswap.i32
   return __bswapd(X);
 }
+TEST_CONSTEXPR(__bswapd(0x00000000) == 0x00000000);
+TEST_CONSTEXPR(__bswapd(0x01020304) == 0x04030201);
 
 int test_bswap(int X) {
 // CHECK-LABEL: test_bswap
 // CHECK: call i32 @llvm.bswap.i32
   return _bswap(X);
 }
+TEST_CONSTEXPR(_bswap(0x00000000) == 0x00000000);
+TEST_CONSTEXPR(_bswap(0x10203040) == 0x40302010);
 
 long test__bswapq(long long X) {
 // CHECK-LABEL: test__bswapq
 // CHECK: call i64 @llvm.bswap.i64
   return __bswapq(X);
 }
+TEST_CONSTEXPR(__bswapq(0x0000000000000000ULL) == 0x0000000000000000);
+TEST_CONSTEXPR(__bswapq(0x0102030405060708ULL) == 0x0807060504030201);
 
 long test_bswap64(long long X) {
 // CHECK-LABEL: test_bswap64
 // CHECK: call i64 @llvm.bswap.i64
   return _bswap64(X);
 }
-
-// Test constexpr handling.
-#if defined(__cplusplus) && (__cplusplus >= 201103L)
-
-char bswapd_0[__bswapd(0x00000000) == 0x00000000 ? 1 : -1];
-char bswapd_1[__bswapd(0x01020304) == 0x04030201 ? 1 : -1];
-
-char bswap_0[_bswap(0x00000000) == 0x00000000 ? 1 : -1];
-char bswap_1[_bswap(0x10203040) == 0x40302010 ? 1 : -1];
-
-char bswapq_0[__bswapq(0x0000000000000000ULL) == 0x0000000000000000 ? 1 : -1];
-char bswapq_1[__bswapq(0x0102030405060708ULL) == 0x0807060504030201 ? 1 : -1];
-
-char bswap64_0[_bswap64(0x0000000000000000ULL) == 0x0000000000000000 ? 1 : -1];
-char bswap64_1[_bswap64(0x1020304050607080ULL) == 0x8070605040302010 ? 1 : -1];
-
-#endif
+TEST_CONSTEXPR(_bswap64(0x0000000000000000ULL) == 0x0000000000000000);
+TEST_CONSTEXPR(_bswap64(0x1020304050607080ULL) == 0x8070605040302010);