user: implement mlibc as the libc, finally.

It's finally done..

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

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

@@ -0,0 +1,22 @@
+#include <assert.h>
+#include <time.h>
+#include <pthread.h>
+
+int variable = 0;
+
+static void *worker(void *arg) {
+	(void) arg;
+	variable = 1;
+	return NULL;
+}
+
+int main() {
+	pthread_t thread;
+	int ret = pthread_create(&thread, NULL, &worker, NULL);
+	assert(!ret);
+
+	ret = pthread_join(thread, NULL);
+	assert(!ret);
+	assert(variable == 1);
+	return 0;
+}