Hurd: fix the _CS_PATH getconf value

Copy sysdeps/unix/confstr.h to avoid using sysdeps/unix/bsd/confstr.h
which adds a non-existing /usr/ucb.

2012-08-30  Pino Toscano  <toscano.pino@tiscali.it>

	* sysdeps/mach/hurd/confstr.h: New file, copied from
	sysdeps/unix/confstr.h.
--- /dev/null
+++ b/sysdeps/mach/hurd/confstr.h
@@ -0,0 +1 @@
+#define	CS_PATH	"/bin:/usr/bin"