Robust mutexes are unsupported

Reverts musl commit 5994de4e02a05c19a6bddadcfb687ab2e7511bd6.

Author: kleisauke

system/lib/libc/musl/src/thread/pthread_mutexattr_setrobust.c

@@ -1,13 +1,15 @@
 #include "pthread_impl.h"
+#ifndef __EMSCRIPTEN__ // XXX Emscripten revert musl commit 5994de4e02a05c19a6bddadcfb687ab2e7511bd6
 #include "syscall.h"
 
 static volatile int check_robust_result = -1;
+#endif
 
 int pthread_mutexattr_setrobust(pthread_mutexattr_t *a, int robust)
 {
 	if (robust > 1U) return EINVAL;
+#ifndef __EMSCRIPTEN__ // XXX Emscripten revert musl commit 5994de4e02a05c19a6bddadcfb687ab2e7511bd6
 	if (robust) {
-#ifndef __EMSCRIPTEN__
 		int r = check_robust_result;
 		if (r < 0) {
 			void *p;
@@ -16,10 +18,10 @@ int pthread_mutexattr_setrobust(pthread_mutexattr_t *a, int robust)
 			a_store(&check_robust_result, r);
 		}
 		if (r) return r;
-#endif
 		a->__attr |= 4;
 		return 0;
 	}
+#endif
 	a->__attr &= ~4;
 	return 0;
 }