Partially undo change that prevented SED, GREP, EGREP and AR from being changed by libtool or autoconf.

configure.ac

@@ -9,29 +9,23 @@ AM_CONFIG_HEADER([config.h])
 AM_MAINTAINER_MODE
 
 dnl SED is mandatory for configure process and libtool.
-dnl Set it now and prevent it from being changed later.
+dnl Set it now, allowing it to be changed later.
 AC_PATH_PROG([SED], [sed], [not_found],
   [$PATH:/usr/bin:/usr/local/bin])
 if test -z "$SED" || test "$SED" = "not_found"; then
   AC_MSG_ERROR([sed not found in PATH. Cannot continue without sed.])
 fi
-ac_cv_prog_sed="$SED"
-ac_cv_prog_SED="$SED"
-AC_SUBST([SED])
 
 dnl GREP is mandatory for configure process and libtool.
-dnl Set it now and prevent it from being changed later.
+dnl Set it now, allowing it to be changed later.
 AC_PATH_PROG([GREP], [grep], [not_found],
   [$PATH:/usr/bin:/usr/local/bin])
 if test -z "$GREP" || test "$GREP" = "not_found"; then
   AC_MSG_ERROR([grep not found in PATH. Cannot continue without grep.])
 fi
-ac_cv_prog_grep="$GREP"
-ac_cv_prog_GREP="$GREP"
-AC_SUBST([GREP])
 
 dnl EGREP is mandatory for configure process and libtool.
-dnl Set it now and prevent it from being changed later.
+dnl Set it now, allowing it to be changed later.
 if echo a | ($GREP -E '(a|b)') >/dev/null 2>&1; then
   AC_MSG_CHECKING([for egrep])
   EGREP="$GREP -E"
@@ -43,9 +37,6 @@ fi
 if test -z "$EGREP" || test "$EGREP" = "not_found"; then
   AC_MSG_ERROR([egrep not found in PATH. Cannot continue without egrep.])
 fi
-ac_cv_prog_egrep="$EGREP"
-ac_cv_prog_EGREP="$EGREP"
-AC_SUBST([EGREP])
 
 dnl AR is mandatory for configure process and libtool.
 dnl This is target dependant, so check it as a tool.
@@ -54,7 +45,6 @@ AC_PATH_TOOL([AR], [ar], [not_found],
 if test -z "$AR" || test "$AR" = "not_found"; then
   AC_MSG_ERROR([ar not found in PATH. Cannot continue without ar.])
 fi
-AC_SUBST([AR])
 
 dnl Fetch c-ares version from ares_version.h
 VERSION=`$SED -ne 's/^#define ARES_VERSION_STR "\(.*\)"/\1/p' ${srcdir}/ares_version.h`