Fix hardcoded grep in editline, were GNU grep is required.

(closes issue #12124)
Reported by: dmartin


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@106842 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/editline/Makefile.in

@@ -4,7 +4,7 @@
 
 OSTYPE=$(shell uname -s)
 define cyg_subst_sys
-	if uname -s | grep -qi cygwin; then \
+	if uname -s | ${GREP} -qi cygwin; then \
 	cat $@ | sed -e s/"sys\.h"/"config.h"/g > $@.copy; \
 	mv --force $@.copy $@; \
 	fi