Switch back to native mutexes on macOS

It seems native mutex performance has improved considerably on Mac
lately, primarily by switching to a different default scheduling
policy. For safety, set this policy explicitly.

The special implementation previously used on Mac is still faster but
suffers a problem when used on realtime audio threads, where they will
not get rescheduled as quickly as when using native mutexes.

Bug: webrtc:10373
Change-Id: Iabf97afc5c2609096331bba0199f433fd26b68b2
Reviewed-on: https://webrtc-review.googlesource.com/c/125186
Commit-Queue: Oskar Sundbom <ossu@webrtc.org>
Reviewed-by: Tommi <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26948}
diff --git a/rtc_base/platform_thread_types.h b/rtc_base/platform_thread_types.h
index 0bc42eb..6b9101e 100644
--- a/rtc_base/platform_thread_types.h
+++ b/rtc_base/platform_thread_types.h
@@ -25,6 +25,9 @@
 #elif defined(WEBRTC_POSIX)
 #include <pthread.h>
 #include <unistd.h>
+#if defined(WEBRTC_MAC)
+#include <pthread_spis.h>
+#endif
 #endif
 // clang-format on