assert: fixed compiler warning with LLVM + x86_64-pc-windows-msvc target.

Fixes #15578.

include/SDL3/SDL_assert.h

@@ -265,7 +265,7 @@ disable assertions.
  */
 #define SDL_NULL_WHILE_LOOP_CONDITION (0)
 
-#elif defined(_MSC_VER)  /* Avoid /W4 warnings. */
+#elif defined(_MSC_VER) && !defined(__clang__)  /* Avoid /W4 warnings. */
 /* "while (0,0)" fools Microsoft's compiler's /W4 warning level into thinking
     this condition isn't constant. And looks like an owl's face! */
 #define SDL_NULL_WHILE_LOOP_CONDITION (0,0)