Enable/silence -Wunused-variable.

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@152329 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/buildit b/lib/buildit
index f84c14c..67d1059 100755
--- a/lib/buildit
+++ b/lib/buildit
@@ -28,7 +28,8 @@
 fi
 
 EXTRA_FLAGS="-std=c++0x -stdlib=libc++ -fstrict-aliasing -Wstrict-aliasing=2 \
-             -Wsign-conversion -Wshadow -Wconversion -Wnewline-eof"
+             -Wsign-conversion -Wshadow -Wconversion -Wunused-variable \
+             -Wnewline-eof"
 
 case $TRIPLE in
   *-apple-*)