Fix -Wunused-const-variable warning when using clang-cl

src/render/direct3d12/SDL_render_d3d12.c

@@ -234,7 +234,7 @@ typedef struct
 
 /* Define D3D GUIDs here so we don't have to include uuid.lib. */
 
-#ifdef __GNUC__
+#if defined(__GNUC__) || defined(__clang__)
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wunused-const-variable"
 #endif
@@ -259,7 +259,7 @@ static const GUID SDL_IID_ID3D12PipelineState = { 0x765a30f3, 0xf624, 0x4c6f, {
 static const GUID SDL_IID_ID3D12Heap = { 0x6b3b2502, 0x6e51, 0x45b3, { 0x90, 0xee, 0x98, 0x84, 0x26, 0x5e, 0x8d, 0xf3 } };
 static const GUID SDL_IID_ID3D12InfoQueue = { 0x0742a90b, 0xc387, 0x483f, { 0xb9, 0x46, 0x30, 0xa7, 0xe4, 0xe6, 0x14, 0x58 } };
 
-#ifdef __GNUC__
+#if defined(__GNUC__) || defined(__clang__)
 #pragma GCC diagnostic pop
 #endif