user: implement mlibc as the libc, finally.

It's finally done..

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

user/include/mlibc/tests/rtld/rtld_next/libbar.c

@@ -0,0 +1,16 @@
+#include <dlfcn.h>
+
+typedef char *charFn(void);
+
+__attribute__((weak))
+char *definedInBoth() {
+	return "bar";
+}
+
+charFn *barGetDefault() {
+	return (charFn *)dlsym(RTLD_DEFAULT, "definedInBoth");
+}
+
+charFn *barGetNext() {
+	return (charFn *)dlsym(RTLD_NEXT, "definedInBoth");
+}