Enable/silence -Wsign-compare.

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@152336 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/buildit b/lib/buildit
index 9b2464a..9a29b8f 100755
--- a/lib/buildit
+++ b/lib/buildit
@@ -30,7 +30,8 @@
 EXTRA_FLAGS="-std=c++0x -stdlib=libc++ -fstrict-aliasing -Wstrict-aliasing=2 \
              -Wsign-conversion -Wshadow -Wconversion -Wunused-variable \
              -Wmissing-field-initializers -Wchar-subscripts -Wmismatched-tags \
-             -Wmissing-braces -Wshorten-64-to-32 -Wsign-compare -Wnewline-eof"
+             -Wmissing-braces -Wshorten-64-to-32 -Wsign-compare \
+             -Wstrict-aliasing=2 -Wnewline-eof"
 
 case $TRIPLE in
   *-apple-*)