user: implement mlibc as the libc, finally.

It's finally done..

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

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

@@ -0,0 +1,36 @@
+#include <signal.h>
+#include <assert.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+static volatile int alarms_fired = 0;
+
+static void sigalrm_handler(int signal) {
+	if(signal == SIGALRM)
+		alarms_fired++;
+}
+
+int main() {
+	signal(SIGALRM, sigalrm_handler);
+
+	alarms_fired = 0;
+
+	unsigned int ret = alarm(10);
+	assert(!ret);
+
+	sleep(1);
+
+	ret = alarm(1);
+	assert(ret == 9);
+
+	sleep(2);
+
+	if(alarms_fired != 1) {
+		fprintf(stderr, "alarm handler fired %u times instead of 1\n", alarms_fired);
+		exit(1);
+	}
+
+	return 0;
+}