user: implement mlibc as the libc, finally.

It's finally done..

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

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

@@ -0,0 +1,54 @@
+#include <assert.h>
+#include <pthread.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <sys/wait.h>
+
+_Atomic int prepare_order = 0;
+_Atomic int parent_order = 0;
+_Atomic int child_order = 0;
+
+static void prepare1() { prepare_order = 1; }
+static void prepare2() { prepare_order = 2; }
+
+static void parent1() { parent_order = 1; }
+static void parent2() { parent_order = 2; }
+
+static void child1() { child_order = 1; }
+static void child2() { child_order = 2; }
+
+int main() {
+	assert(!pthread_atfork(prepare1, parent1, child1));
+	assert(!pthread_atfork(prepare2, parent2, child2));
+
+	pid_t pid = fork();
+	assert(pid >= 0);
+
+	if (!pid) {
+		assert(child_order == 2);
+		exit(0);
+	} else {
+		assert(prepare_order == 1);
+		assert(parent_order == 2);
+
+		while (1) {
+			int status = 0;
+
+			int ret = waitpid(pid, &status, 0);
+
+			if (ret == -1 && errno == EINTR)
+				continue;
+
+			assert(ret > 0);
+
+			if (WIFSIGNALED(status) && WTERMSIG(status) == SIGABRT)
+				return 1;
+
+			return WEXITSTATUS(status);
+		}
+	}
+
+	return 0;
+}