winsup/doc: Fix xidepend to handle relative pathnames

It seems that xidepend doesn't work correctly if we are ./configure'd using a
relative pathname to the srcdir:

$ make
cd ../../../../src/winsup/doc && ./xidepend ../../../../src/winsup/doc/cygwin-ug-net.xml ../../../../src/winsup/doc/cygwin-api.xml >"/wip/cygwin/build/x86_64-unknown-cygwin/winsup/doc/Makefile.dep"
grep: ../../../../src/winsup/doc/cygwin-ug-net.xml: No such file or directory
grep: ../../../../src/winsup/doc/cygwin-api.xml: No such file or directory

Although it might be better to fix this by making xidepend use pathnames, rather
than ignoring them and assuming everything is in the current directory...

2015-06-12  Jon Turney  <jon.turney@dronecode.org.uk>

	* xidepend: Fix to handle relative pathnames.

Signed-off-by: Jon TURNEY <jon.turney@dronecode.org.uk>

winsup/doc/ChangeLog

@@ -1,3 +1,7 @@
+2015-06-12  Jon Turney  <jon.turney@dronecode.org.uk>
+
+	* xidepend: Fix to handle relative pathnames.
+
 2015-06-12  Jon Turney  <jon.turney@dronecode.org.uk>
 
 	* Makefile.in (.PHONY): Remove tarball target.

winsup/doc/xidepend

@@ -11,6 +11,7 @@ fi
 
 for f in "$@"
 do
+	f=`basename "$f"`
 	if fgrep -q 'xi:include' "$f"
 	then
 		# This file uses XIncludes.  Let's chase its deps recursively.