CompilerTestCodeGenFloatingPointEnvironment fails on ARM64x when run under x64 emulation

Start in tools/clang/unittests/HLSL/CompilerTest.cpp at CompilerTest::CodeGenFloatingPointEnvironment and review its existing Win32 guards. Run the test under x64 emulation on Windows ARM64 and verify that runtime detection skips only that case while preserving compatibility on older Windows versions and other platforms.

Description
CodeGenFloatingPointEnvironment is a win32 only test as guarded by defines here:
https://github.com/microsoft/DirectXShaderCompiler/blob/c1104ee6ff393378f9d75f3326d5c56fac8e95b7/tools/clang/unittests/HLSL/CompilerTest.cpp#L4405

This doesn't appropriately guard against running the x64 version of this test on an ARM64 machine though.
So, this test fails in arm64x pipelines when targeting x64.

StartGroup: CompilerTest::CodeGenFloatingPointEnvironment

Verify: IsTrue(_controlfp_s(&fpOriginal, 0, 0) == 0)

Verify: IsTrue(_controlfp_s(&fpSavedState, 0, 0) == 0)

Verify: IsTrue(_controlfp_s(&newValue, fpTestState, fpTestMask) == 0)

Verify: IsTrue(_controlfp_s(&fpBeforeCompile, 0, 0) == 0)

Error: Verify: AreEqual((fpBeforeCompile & fpTestMask), fpTestState) - Values (34079263, 34079255) [File: C:\__w\1\s\DirectXShaderCompiler\tools\clang\unittests\HLSL\CompilerTest.cpp, 
Function: CompilerTest::CodeGenFloatingPointEnvironment, Line: 4377]

EndGroup: CompilerTest::CodeGenFloatingPointEnvironment [Failed]

Environment

• DXC version: 1.9.2607
• Host Operating System: Windows ARM64

How to fix
We will need to add runtime detection to skip this test. Copilot had a few suggestions that wouldn't work. And then arrived at this, which I think will work. But we'll want to verify it.
https://learn.microsoft.com/en-us/windows/win32/api/wow64apiset/nf-wow64apiset-iswow64process2

static bool IsX64EmulatedOnArm64() {
  using Fn = BOOL(WINAPI *)(HANDLE, USHORT *, USHORT *);

  auto fn = reinterpret_cast<Fn>(GetProcAddress(
      GetModuleHandleW(L"kernel32.dll"), "IsWow64Process2"));
  if (!fn)
    return false;

  USHORT processMachine = 0;
  USHORT nativeMachine = 0;
  return fn(GetCurrentProcess(), &processMachine, &nativeMachine) &&
         processMachine == IMAGE_FILE_MACHINE_AMD64 &&
         nativeMachine == IMAGE_FILE_MACHINE_ARM64;
}

Dynamic lookup preserves compatibility with Windows versions predating  IsWow64Process2 . This detects the exact failing case: x64 TAEF running through emulation on ARM64.