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

fusl/src/stdio/fseek.c

Index: fusl/src/stdio/fseek.c
diff --git a/fusl/src/stdio/fseek.c b/fusl/src/stdio/fseek.c
new file mode 100644
index 0000000000000000000000000000000000000000..b160b74edca0db9eeb8599a268a9ffc469d1aeb3
--- /dev/null
+++ b/fusl/src/stdio/fseek.c
@@ -0,0 +1,43 @@
+#include "stdio_impl.h"
+
+int __fseeko_unlocked(FILE *f, off_t off, int whence)
+{
+	/* Adjust relative offset for unread data in buffer, if any. */
+	if (whence == SEEK_CUR) off -= f->rend - f->rpos;
+
+	/* Flush write buffer, and report error on failure. */
+	if (f->wpos > f->wbase) {
+		f->write(f, 0, 0);
+		if (!f->wpos) return -1;
+	}
+
+	/* Leave writing mode */
+	f->wpos = f->wbase = f->wend = 0;
+
+	/* Perform the underlying seek. */
+	if (f->seek(f, off, whence) < 0) return -1;
+
+	/* If seek succeeded, file is seekable and we discard read buffer. */
+	f->rpos = f->rend = 0;
+	f->flags &= ~F_EOF;
+	
+	return 0;
+}
+
+int __fseeko(FILE *f, off_t off, int whence)
+{
+	int result;
+	FLOCK(f);
+	result = __fseeko_unlocked(f, off, whence);
+	FUNLOCK(f);
+	return result;
+}
+
+int fseek(FILE *f, long off, int whence)
+{
+	return __fseeko(f, off, whence);
+}
+
+weak_alias(__fseeko, fseeko);
+
+LFS64(fseeko);