D3D12: Silence `-Wmaybe-uninitialized` warning in D3D12MemAlloc

This was lost in #104893 when removing the warning ignores no longer relevant
when including the D3D12MemAlloc _header_ as external.
But we still compile the .cpp directly and it has this warning.

Clarified why have a wrapper for this file.

drivers/d3d12/d3d12ma.cpp

@@ -28,6 +28,14 @@
 /* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                 */
 /**************************************************************************/
 
-#include "rendering_context_driver_d3d12.h"
+// Wrapper needed to set the required rpcndr version for MinGW compatibility.
+// Since we're compiling thirdparty code in a Godot SCons environment with
+// warnings enabled, we also need to silence them manually.
+
+#include "rendering_device_driver_d3d12.h" // For __REQUIRED_RPCNDR_H_VERSION__.
+
+GODOT_GCC_WARNING_PUSH_AND_IGNORE("-Wmaybe-uninitialized")
 
 #include <D3D12MemAlloc.cpp>
+
+GODOT_GCC_WARNING_POP