Fix the msvs 2010 build.

Fix the msvs 2010 build.

The Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 16.00.30319.01
implements parts of C++0x based on the draft standard. An old version of
the draft had a bug that makes std::pair<T1*, T2*>(something, 0) fail to
compile. This is because the template<class U, class V> pair(U&& x, V&& y)
constructor is selected, even though it later fails to implicitly convert
U and V to frist_type and second_type.

This has been fixed in n3090, but it seems that Microsoft is not going to
update msvc.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112257 91177308-0d34-0410-b5e6-96231b3b80d8