user: implement mlibc as the libc, finally.

It's finally done..

Signed-off-by: kaguya <vpshinomiya@protonmail.com>

user/include/mlibc/tests/posix/pthread_cleanup.c

@@ -0,0 +1,42 @@
+#include <stdint.h>
+#include <assert.h>
+#include <pthread.h>
+
+_Atomic uintptr_t cleanup_val = 0;
+
+static void cleanup(void *arg) {
+	cleanup_val = (uintptr_t)arg;
+}
+
+static void *worker(void *arg) {
+	(void)arg;
+
+	pthread_cleanup_push(cleanup, (void *)1);
+	pthread_cleanup_push(cleanup, (void *)2);
+	pthread_cleanup_push(cleanup, (void *)3);
+	pthread_cleanup_push(cleanup, (void *)4);
+
+	pthread_cleanup_pop(1);
+	assert(cleanup_val == 4);
+
+	pthread_cleanup_pop(0);
+	assert(cleanup_val == 4);
+
+	pthread_exit(NULL);
+
+	pthread_cleanup_pop(0);
+	pthread_cleanup_pop(0);
+
+	return NULL;
+}
+
+int main() {
+	pthread_t thread;
+	assert(!pthread_create(&thread, NULL, &worker, NULL));
+	assert(!pthread_join(thread, NULL));
+
+	assert(cleanup_val == 1);
+
+	return 0;
+}
+