user: implement mlibc as the libc, finally.

It's finally done..

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

user/include/mlibc/tests/glibc/linux-syscall.c

@@ -0,0 +1,14 @@
+#include <sys/syscall.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+
+int main() {
+	char *data = "hello mlibc\n";
+	long ret = syscall(SYS_write, 1, data, strlen(data));
+	assert(ret == (long)strlen(data));
+
+	syscall(SYS_exit, 0);
+	abort();
+}