Merge #19594

19594: sys: drop broken and legacy Mac OS handling r=maribu a=maribu

### Contribution description

This drops special handling for Mac OS (X) `native`, which is not supported anymore anyway and causing issues when building for non-`native` targets on Mac OS.


Co-authored-by: Marian Buschsieweke <marian.buschsieweke@ovgu.de>

sys/include/byteorder.h

@@ -23,10 +23,6 @@
 #include <stdint.h>
 #include "unaligned.h"
 
-#if defined(__MACH__)
-#   include "clang_compat.h"
-#endif
-
 #ifdef __cplusplus
 extern "C" {
 #endif

sys/posix/pthread/include/pthread_cond.h

@@ -26,14 +26,6 @@
 #   include <sys/types.h>
 #endif
 
-#ifdef __MACH__
-/* needed for AVAILABLE_MAC_OS_X_VERSION_10_12_AND_LATER */
-#include <AvailabilityMacros.h>
-#if !defined(AVAILABLE_MAC_OS_X_VERSION_10_12_AND_LATER)
-typedef int clockid_t;
-#endif
-#endif
-
 #ifdef __cplusplus
 extern "C" {
 #endif