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

fusl/src/stdio/__stdio_seek.c

Index: fusl/src/stdio/__stdio_seek.c
diff --git a/fusl/src/stdio/__stdio_seek.c b/fusl/src/stdio/__stdio_seek.c
new file mode 100644
index 0000000000000000000000000000000000000000..13e06a663eff8e4cb79cabf33c4ec08df20e570e
--- /dev/null
+++ b/fusl/src/stdio/__stdio_seek.c
@@ -0,0 +1,13 @@
+#include "stdio_impl.h"
+
+off_t __stdio_seek(FILE *f, off_t off, int whence)
+{
+	off_t ret;
+#ifdef SYS__llseek
+	if (syscall(SYS__llseek, f->fd, off>>32, off, &ret, whence)<0)
+		ret = -1;
+#else
+	ret = syscall(SYS_lseek, f->fd, off, whence);
+#endif
+	return ret;
+}