Cement ABI on clang for char16_t and char32_t.  Also fixed some comments in <iterator>.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@113842 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/buildit b/lib/buildit
index 4b07113..0b51b2d 100755
--- a/lib/buildit
+++ b/lib/buildit
@@ -14,7 +14,7 @@
 
 if [ -z "$CXX" ]
 then
-	CXX=g++
+	CXX=clang++
 fi
 
 if [ -z $MACOSX_DEPLOYMENT_TARGET ]