configure: use `$EGREP` in place of `grep -E`

`$EGREP` is set based on an earlier test in configure so that we can
work with systems that have `egrep` and a `grep` that does not support
`-E`.

Closes #13780

diff --git a/configure.ac b/configure.ac
index a4ea9f72d6fc6ddb38c9d7fe1bb4cab9cf9f5143..646c255b99e955409b3980b0bdd0b2c9bde2ffd3 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -5037,7 +5037,7 @@ AC_MSG_NOTICE([Configured to build curl/libcurl:
   Features:         ${SUPPORT_FEATURES}
 ])
 
-non13=`echo "$TLSCHOICE" | grep -Ei 'bearssl|secure-transport|mbedtls'`;
+non13=`echo "$TLSCHOICE" | $EGREP -i 'bearssl|secure-transport|mbedtls'`;
 if test -n "$non13"; then
  cat >&2 << _EOF
   WARNING: A selected TLS library ($TLSCHOICE) does not support TLS 1.3!