user: implement mlibc as the libc, finally.

It's finally done..

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

user/include/mlibc/tests/rtld/ifunc-dlopen/lib.c

@@ -0,0 +1,11 @@
+#include <stdint.h>
+
+static uint64_t foo_impl(void) {
+    return 69;
+}
+
+static uint64_t (*foo_resolver(void))(void) {
+    return foo_impl;
+}
+
+uint64_t foo(void) __attribute__((ifunc("foo_resolver")));