SDL_stdinc.h (SDL_COMPILE_TIME_ASSERT): Keep C++ case alone (after PR/10331)

Some versions of gcc will define __STDC_VERSION__ even when compiling in C++ mode.
Reference issue: https://github.com/libsdl-org/SDL/issues/6078 which was fixed by
https://github.com/libsdl-org/SDL/commit/f6b81125b340e00129978f2c9eebfba6a4d25692

(cherry picked from commit 70c1012e8c76a662bb59554e4be8f9660e2b5708)
(cherry picked from commit 86b4d035dbc538db3cb6f41fe4ddaaab9bd2cf64)

include/SDL_stdinc.h

@@ -376,7 +376,12 @@ typedef uint64_t Uint64;
 #endif /* SDL_DISABLE_ANALYZE_MACROS */
 
 #ifndef SDL_COMPILE_TIME_ASSERT
-#if (defined(__cplusplus) && __cplusplus >= 201103L) || (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202311L)
+#if defined(__cplusplus)
+/* Keep C++ case alone: Some versions of gcc will define __STDC_VERSION__ even when compiling in C++ mode. */
+#if (__cplusplus >= 201103L)
+#define SDL_COMPILE_TIME_ASSERT(name, x)  static_assert(x, #x)
+#endif
+#elif defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 202311L)
 #define SDL_COMPILE_TIME_ASSERT(name, x)  static_assert(x, #x)
 #elif defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 201112L)
 #define SDL_COMPILE_TIME_ASSERT(name, x) _Static_assert(x, #x)