libc: pthread: implement mutexes

lib/libc/pthread/mutex/pthread_mutex_trylock.c

@@ -0,0 +1,18 @@
+#include <errno.h>
+#include <pthread.h>
+
+int pthread_mutex_trylock(pthread_mutex_t *mut)
+{
+	kern_futex_t expected = 0;
+	if (__atomic_compare_exchange_n(
+		    &mut->__v,
+		    &expected,
+		    1,
+		    0,
+		    __ATOMIC_ACQUIRE,
+		    __ATOMIC_ACQUIRE)) {
+		return 0;
+	}
+
+	return __set_errno(EBUSY);
+}