The C standard defines a boolean expression as a signed integer value.

Microsoft came to the same conclusion:
https://devblogs.microsoft.com/oldnewthing/20110328-00/?p=11113

Fixes https://github.com/libsdl-org/SDL/issues/8761

include/SDL3/SDL_stdinc.h

@@ -133,7 +133,7 @@ char *alloca();
  */
 #define SDL_FALSE 0
 #define SDL_TRUE 1
-typedef unsigned int SDL_bool;
+typedef int SDL_bool;
 
 /**
  * A signed 8-bit integer type.