configure: add getdelim() check

As an optimization, strbuf will take advantage of getdelim() if
available, so add a configure check which defines HAVE_GETDELIM if
found.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

configure.ac

@@ -1041,6 +1041,12 @@ GIT_CHECK_FUNC(initgroups,
 [NO_INITGROUPS=YesPlease])
 GIT_CONF_SUBST([NO_INITGROUPS])
 #
+# Define HAVE_GETDELIM if you have getdelim in the C library.
+GIT_CHECK_FUNC(getdelim,
+[HAVE_GETDELIM=YesPlease],
+[HAVE_GETDELIM=])
+GIT_CONF_SUBST([HAVE_GETDELIM])
+#
 #
 # Define NO_MMAP if you want to avoid mmap.
 #