user: implement mlibc as the libc, finally.

It's finally done..

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

user/include/mlibc/sysdeps/aero/generic/entry.cpp

@@ -0,0 +1,17 @@
+#include <bits/ensure.h>
+#include <mlibc/elf/startup.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+extern "C" uintptr_t *__dlapi_entrystack();
+
+extern char **environ;
+
+extern "C" void __mlibc_entry(int (*main_fn)(int argc, char *argv[],
+                                             char *env[])) {
+    // TODO: call __dlapi_enter, otherwise static builds will break (see Linux
+    // sysdeps)
+    auto result =
+        main_fn(mlibc::entry_stack.argc, mlibc::entry_stack.argv, environ);
+    exit(result);
+}