Add a "fork" of musl as //fusl.

fusl/src/stdio/__stdio_exit.c

+#include "stdio_impl.h"
+
+static FILE *volatile dummy_file = 0;
+weak_alias(dummy_file, __stdin_used);
+weak_alias(dummy_file, __stdout_used);
+weak_alias(dummy_file, __stderr_used);
+
+static void close_file(FILE *f)
+{
+        if (!f) return;
+        FFINALLOCK(f);
+        if (f->wpos > f->wbase) f->write(f, 0, 0);
+        if (f->rpos < f->rend) f->seek(f, f->rpos-f->rend, SEEK_CUR);
+}
+
+void __stdio_exit(void)
+{
+        FILE *f;
+        for (f=*__ofl_lock(); f; f=f->next) close_file(f);
+        close_file(__stdin_used);
+        close_file(__stdout_used);
+}
+
+weak_alias(__stdio_exit, __stdio_exit_needed);