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

fusl/src/stdio/__towrite.c

Index: fusl/src/stdio/__towrite.c
diff --git a/fusl/src/stdio/__towrite.c b/fusl/src/stdio/__towrite.c
new file mode 100644
index 0000000000000000000000000000000000000000..0a69d926dc3c10547a00ae9f7b8517c188078c68
--- /dev/null
+++ b/fusl/src/stdio/__towrite.c
@@ -0,0 +1,25 @@
+#include "stdio_impl.h"
+
+int __towrite(FILE *f)
+{
+	f->mode |= f->mode-1;
+	if (f->flags & (F_NOWR)) {
+		f->flags |= F_ERR;
+		return EOF;
+	}
+	/* Clear read buffer (easier than summoning nasal demons) */
+	f->rpos = f->rend = 0;
+
+	/* Activate write through the buffer. */
+	f->wpos = f->wbase = f->buf;
+	f->wend = f->buf + f->buf_size;
+
+	return 0;
+}
+
+void __stdio_exit_needed(void);
+
+void __towrite_needs_stdio_exit()
+{
+	__stdio_exit_needed();
+}