include: Renamed begin_code.h and close_code.h to have SDL_ prefixes.

Fixes #6864.

include/SDL3/SDL_endian.h

@@ -110,7 +110,7 @@ _m_prefetch(void *__P)
 #endif /* !SDL_FLOATWORDORDER */
 
 
-#include <SDL3/begin_code.h>
+#include <SDL3/SDL_begin_code.h>
 /* Set up for C function definitions, even when using C++ */
 #ifdef __cplusplus
 extern "C" {
@@ -341,7 +341,7 @@ SDL_SwapFloat(float x)
 #ifdef __cplusplus
 }
 #endif
-#include <SDL3/close_code.h>
+#include <SDL3/SDL_close_code.h>
 
 #endif /* SDL_endian_h_ */