./config: detect x32-only environment.

RT#4583
Reviewed-by: NRich Salz <rsalz@openssl.org>

config

@@ -640,7 +640,12 @@ case "$GUESSOS" in
 	#fi
 	OUT="linux64-s390x"
 	;;
-  x86_64-*-linux?) OUT="linux-x86_64" ;;
+  x86_64-*-linux?)
+	if $CC -dM -E -x c /dev/null 2>&1 | grep -q ILP32 > /dev/null; then
+	    OUT="linux-x32"
+	else
+	    OUT="linux-x86_64"
+	fi ;;
   *86-*-linux2) OUT="linux-elf"
 	if [ "$GCCVER" -gt 28 ]; then
           if grep '^model.*Pentium' /proc/cpuinfo >/dev/null ; then