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

fusl/src/stdio/__stdio_write.c

Index: fusl/src/stdio/__stdio_write.c
diff --git a/fusl/src/stdio/__stdio_write.c b/fusl/src/stdio/__stdio_write.c
new file mode 100644
index 0000000000000000000000000000000000000000..d2d89475b0f9429dca8b538b689f97c27bbe5fee
--- /dev/null
+++ b/fusl/src/stdio/__stdio_write.c
@@ -0,0 +1,34 @@
+#include "stdio_impl.h"
+#include <sys/uio.h>
+
+size_t __stdio_write(FILE *f, const unsigned char *buf, size_t len)
+{
+	struct iovec iovs[2] = {
+		{ .iov_base = f->wbase, .iov_len = f->wpos-f->wbase },
+		{ .iov_base = (void *)buf, .iov_len = len }
+	};
+	struct iovec *iov = iovs;
+	size_t rem = iov[0].iov_len + iov[1].iov_len;
+	int iovcnt = 2;
+	ssize_t cnt;
+	for (;;) {
+		cnt = syscall(SYS_writev, f->fd, iov, iovcnt);
+		if (cnt == rem) {
+			f->wend = f->buf + f->buf_size;
+			f->wpos = f->wbase = f->buf;
+			return len;
+		}
+		if (cnt < 0) {
+			f->wpos = f->wbase = f->wend = 0;
+			f->flags |= F_ERR;
+			return iovcnt == 2 ? 0 : len-iov[0].iov_len;
+		}
+		rem -= cnt;
+		if (cnt > iov[0].iov_len) {
+			cnt -= iov[0].iov_len;
+			iov++; iovcnt--;
+		}
+		iov[0].iov_base = (char *)iov[0].iov_base + cnt;
+		iov[0].iov_len -= cnt;
+	}
+}