user: implement mlibc as the libc, finally.

It's finally done..

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

user/include/mlibc/tests/rtld/scope1/libfoo.c

@@ -0,0 +1,9 @@
+char *foo(void) {
+	return "foo";
+}
+
+char global[] = "foo global";
+
+char *foo_global(void) {
+	return global;
+}