noexcept for <utility>.  This included a little repair on pair, and some noexcept workarounds.

llvm-svn: 132186
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: a676f7d36a062cd74f471268c241ebc326f6c861
diff --git a/include/algorithm b/include/algorithm
index 4909221..4789b0b 100644
--- a/include/algorithm
+++ b/include/algorithm
@@ -1659,13 +1659,7 @@
 
 // iter_swap
 
-template <class _ForwardIterator1, class _ForwardIterator2>
-inline _LIBCPP_INLINE_VISIBILITY
-void
-iter_swap(_ForwardIterator1 __a, _ForwardIterator2 __b)
-{
-    swap(*__a, *__b);
-}
+// moved to <type_traits> for better swap / noexcept support
 
 // transform