--- a/build-aux/config.guess	Sun May 20 14:02:19 2018 +0200
+++ b/build-aux/config.guess	Sun May 20 06:49:39 2018 -0700
@@ -2,7 +2,7 @@
 # Attempt to guess a canonical system name.
 #   Copyright 1992-2018 Free Software Foundation, Inc.
 
-timestamp='2018-03-08'
+timestamp='2018-05-19'
 
 # This file is free software; you can redistribute it and/or modify it
 # under the terms of the GNU General Public License as published by
@@ -106,7 +106,7 @@
  { echo "$me: cannot create a temporary directory in $TMPDIR" >&2 ; exit 1 ; } ;
 dummy=$tmp/dummy ;
 tmpfiles="$dummy.c $dummy.o $dummy.rel $dummy" ;
-case $CC_FOR_BUILD,$HOST_CC,$CC in
+case ${CC_FOR_BUILD-},${HOST_CC-},${CC-} in
  ,,)    echo "int x;" > "$dummy.c" ;
 	for c in cc gcc c89 c99 ; do
 	  if ($c -c -o "$dummy.o" "$dummy.c") >/dev/null 2>&1 ; then
@@ -237,7 +237,7 @@
 	# Since CPU_TYPE-MANUFACTURER-KERNEL-OPERATING_SYSTEM:
 	# contains redundant information, the shorter form:
 	# CPU_TYPE-MANUFACTURER-OPERATING_SYSTEM is used.
-	echo "$machine-${os}${release}${abi}"
+	echo "$machine-${os}${release}${abi-}"
 	exit ;;
     *:Bitrig:*:*)
 	UNAME_MACHINE_ARCH=`arch | sed 's/Bitrig.//'`