user: implement mlibc as the libc, finally.

It's finally done..

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

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

@@ -0,0 +1,46 @@
+#include <assert.h>
+#include <pthread.h>
+#include <signal.h>
+
+_Atomic int handler_ready = 0;
+_Atomic int thread_signal_ran = 0;
+
+static void sig_handler(int sig, siginfo_t *info, void *ctx) {
+	(void)sig;
+	(void)info;
+	(void)ctx;
+
+	thread_signal_ran = 1;
+}
+
+static void *worker(void *arg) {
+	(void)arg;
+
+	struct sigaction sa;
+	sigemptyset(&sa.sa_mask);
+	sa.sa_sigaction = sig_handler;
+	sa.sa_flags = SA_SIGINFO;
+	assert(!sigaction(SIGUSR1, &sa, NULL));
+
+	handler_ready = 1;
+
+	while (!thread_signal_ran)
+		;
+
+	return NULL;
+}
+
+int main() {
+	pthread_t thread;
+	assert(!pthread_create(&thread, NULL, &worker, NULL));
+
+	while (!handler_ready)
+		;
+
+	assert(!pthread_kill(thread, SIGUSR1));
+	assert(!pthread_join(thread, NULL));
+
+	assert(thread_signal_ran);
+
+	return 0;
+}