llvm/cmake/config.guess: add support for e2k (Elbrus-2000) (#162460)

Backport patch from gnu-config:
https://lists.gnu.org/archive/html/config-patches/2015-03/msg00000.html

Author: r-a-sattarov

llvm/cmake/config.guess

@@ -908,6 +908,9 @@ EOF
     crisv32:Linux:*:*)
 	echo crisv32-axis-linux-gnu
 	exit ;;
+    e2k:Linux:*:*)
+	echo ${UNAME_MACHINE}-unknown-linux-gnu
+	exit ;;
     frv:Linux:*:*)
 	echo frv-unknown-linux-gnu
 	exit ;;