user: implement mlibc as the libc, finally.

It's finally done..

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

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

@@ -0,0 +1,22 @@
+#include <assert.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+siginfo_t si;
+
+int main() {
+	int pid = fork();
+
+	if(!pid)
+		exit(69);
+
+	int ret = waitid(P_ALL, 0, &si, WEXITED);
+	assert(ret == 0);
+	assert(si.si_pid == pid);
+	assert(si.si_signo == SIGCHLD);
+	assert(si.si_code == CLD_EXITED);
+
+	return 0;
+}