Removed SDL_bool in favor of plain bool

We require stdbool.h in the build environment, so we might as well use the plain bool type.

If your environment doesn't have stdbool.h, this simple replacement will suffice:
typedef signed char bool;

test/testgles2.c

@@ -66,7 +66,7 @@ typedef struct thread_data
 static SDLTest_CommonState *state;
 static SDL_GLContext *context = NULL;
 static int depth = 16;
-static SDL_bool suspend_when_occluded;
+static bool suspend_when_occluded;
 static GLES2_Context ctx;
 static shader_data *datas;
 
@@ -699,7 +699,7 @@ int main(int argc, char *argv[])
                 ++threaded;
                 consumed = 1;
             } else if(SDL_strcasecmp(argv[i], "--suspend-when-occluded") == 0) {
-                suspend_when_occluded = SDL_TRUE;
+                suspend_when_occluded = true;
                 consumed = 1;
             } else if (SDL_strcasecmp(argv[i], "--zdepth") == 0) {
                 i++;