Fix SDL_HINT_THREAD_FORCE_REALTIME_TIME_CRITICAL also applying to HIGH priorities

As the name suggests, the hint should only apply to SDL_THREAD_PRIORITY_TIME_CRITICAL

The resulting priorities for my current distro result in these values:

     | High         | Time Critical
Hint |--------------|-----------------
 0   |  P=10 N=-10  | P=5   N=-15
 1   |  P=10 N=-10  | P=-21 N=0

include/SDL_hints.h

@@ -801,7 +801,7 @@ extern "C" {
 *  Currently no other platform hint values are defined but may be in the future.
 *
 *  \note On Linux, the kernel may send SIGKILL to realtime tasks which exceed the distro
-*  configured execution budget for rtkit. This budget is queriably through RLIMIT_RTTIME
+*  configured execution budget for rtkit. This budget can be queried through RLIMIT_RTTIME
 *  after calling SDL_SetThreadPriority().
 */
 #define SDL_HINT_THREAD_PRIORITY_POLICY         "SDL_THREAD_PRIORITY_POLICY"

src/thread/pthread/SDL_systhread.c

@@ -208,7 +208,7 @@ SDL_SYS_SetThreadPriority(SDL_ThreadPriority priority)
     int pri_policy;
     pthread_t thread = pthread_self();
     const char *policyhint = SDL_GetHint(SDL_HINT_THREAD_PRIORITY_POLICY);
-    const SDL_bool allow_realtime_hint = SDL_GetHintBoolean(SDL_HINT_THREAD_FORCE_REALTIME_TIME_CRITICAL, SDL_FALSE);
+    const SDL_bool timecritical_realtime_hint = SDL_GetHintBoolean(SDL_HINT_THREAD_FORCE_REALTIME_TIME_CRITICAL, SDL_FALSE);
 
     if (pthread_getschedparam(thread, &policy, &sched) != 0) {
         return SDL_SetError("pthread_getschedparam() failed");
@@ -229,7 +229,7 @@ SDL_SYS_SetThreadPriority(SDL_ThreadPriority priority)
         pri_policy = SCHED_RR;
         break;
 #else
-        pri_policy = allow_realtime_hint ? SCHED_RR : SCHED_OTHER;
+        pri_policy = SCHED_OTHER;
         break;
 #endif
     default:
@@ -237,6 +237,10 @@ SDL_SYS_SetThreadPriority(SDL_ThreadPriority priority)
         break;
     }
 
+    if (timecritical_realtime_hint && priority == SDL_THREAD_PRIORITY_TIME_CRITICAL) {
+        pri_policy = SCHED_RR;
+    }
+
     if (policyhint) {
         if (SDL_strcmp(policyhint, "current") == 0) {
             /* Leave current thread scheduler policy unchanged */