core: Expose API to elevate a thread to realtime priority

This should make it easier for clients to elevate their audio threads to
real time priority without having to dig through much through specific
system internals.

src/pulse/util.h

@@ -54,6 +54,12 @@ char *pa_path_get_filename(const char *p);
 /** Wait t milliseconds */
 int pa_msleep(unsigned long t);
 
+/** Make the calling thread realtime if we can. On Linux, this uses RealTimeKit
+ * if available and POSIX APIs otherwise (the latter applies to other UNIX
+ * variants as well). This is also implemented for macOS and Windows.
+ * \since 13.0 */
+int pa_thread_make_realtime(int rtprio);
+
 PA_C_DECL_END
 
 #endif