ape/lib9: expose fd2path (thanks phil9)

Fd2path is a useful call for the netsurf plan9 frontend,
so we should expose it.

sys/include/ape/lib9.h

@@ -74,5 +74,6 @@ extern	unsigned long	getfcr(void);
 extern	unsigned long	getfsr(void);
 extern	void		setfcr(unsigned long);
 extern	void		setfsr(unsigned long);
+extern	int 	fd2path(int, char*, int);
 
 #endif

sys/src/ape/lib/9/fd2path.c

@@ -0,0 +1,9 @@
+#include <lib9.h>
+
+extern	int	_FD2PATH(int, char*, int);
+
+int
+fd2path(int fd, char *buf, int nbuf)
+{
+	return _FD2PATH(fd, buf, nbuf);
+}

sys/src/ape/lib/9/mkfile

@@ -28,6 +28,7 @@ OFILES=\
 	u32.$O\
 	u64.$O\
 	unmount.$O\
+	fd2path.$O\
 
 </sys/src/cmd/mksyslib