m[mutex] Remove busyloop mutex implemenation

Don't know why I ever added this. :)

configure.ac

@@ -449,11 +449,6 @@ if $hb_cv_have_solaris_atomic_ops; then
 	AC_DEFINE(HAVE_SOLARIS_ATOMIC_OPS, 1, [Have Solaris __machine_*_barrier and atomic_* operations])
 fi
 
-if test "$os_win32" = no && ! $have_pthread; then
-	AC_CHECK_HEADERS(sched.h)
-	AC_SEARCH_LIBS(sched_yield,rt,AC_DEFINE(HAVE_SCHED_YIELD, 1, [Have sched_yield]))
-fi
-
 dnl ===========================================================================
 
 AC_CONFIG_FILES([

meson.build

@@ -285,9 +285,6 @@ if host_machine.system() != 'windows'
 
   if thread_dep.found()
     conf.set('HAVE_PTHREAD', 1)
-  else
-    check_headers += ['sched.h']
-    check_funcs += ['sched_yield', {'link_with': 'rt'}]
   endif
 endif
 

src/hb-mutex.hh

@@ -73,24 +73,6 @@ typedef CRITICAL_SECTION hb_mutex_impl_t;
 #define hb_mutex_impl_finish(M)	DeleteCriticalSection (M)
 
 
-#elif !defined(HB_NO_MT) && defined(HAVE_INTEL_ATOMIC_PRIMITIVES)
-
-#if defined(HAVE_SCHED_H) && defined(HAVE_SCHED_YIELD)
-# include <sched.h>
-# define HB_SCHED_YIELD() sched_yield ()
-#else
-# define HB_SCHED_YIELD() HB_STMT_START {} HB_STMT_END
-#endif
-
-/* This actually is not a totally awful implementation. */
-typedef volatile int hb_mutex_impl_t;
-#define HB_MUTEX_IMPL_INIT	0
-#define hb_mutex_impl_init(M)	*(M) = 0
-#define hb_mutex_impl_lock(M)	HB_STMT_START { while (__sync_lock_test_and_set((M), 1)) HB_SCHED_YIELD (); } HB_STMT_END
-#define hb_mutex_impl_unlock(M)	__sync_lock_release (M)
-#define hb_mutex_impl_finish(M)	HB_STMT_START {} HB_STMT_END
-
-
 #elif defined(HB_NO_MT)
 
 typedef int hb_mutex_impl_t;