Merging r226124:

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r226124 | hans | 2015-01-14 23:36:20 -0500 (Wed, 14 Jan 2015) | 2 lines

utils/release/tag.sh: fix -revision vs. -rc check

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llvm-svn: 237015
diff --git a/llvm/utils/release/tag.sh b/llvm/utils/release/tag.sh
index 2dfba04..503413b 100755
--- a/llvm/utils/release/tag.sh
+++ b/llvm/utils/release/tag.sh
@@ -117,7 +117,7 @@
 if [ "x$rc" = "x" ]; then
     tag_version
 else
-    if [ "x$revision" != "x" ]; then
+    if [ "$revision" != "HEAD" ]; then
         echo "error: cannot use -revision with -rc"
         echo
         usage