LibC: implement and call __cxa_finalize() on exit()

This allows global destructors to be actually called

libc/include/icxxabi.h

@@ -0,0 +1,10 @@
+#pragma once
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+int __cxa_atexit(void (*func)(void*), void* data, void* dso_handle);
+void __cxa_finalize(void* func);
+
+__END_DECLS