[boost] [config] Patch for clang.hpp to support clang in Windows using VC++ RTL

Subject: [boost] [config] Patch for clang.hpp to support clang in Windows using VC++ RTL
From: Edward Diener (eldiener_at_[hidden])
Date: 2013-10-13 21:52:14

Once Boost 1.55 is out the doors can I apply the attached patch for 
clang when _MSC_VER is defined ? Unfortunately clang in this situation 
does not currently support the C++11 types char16_t or char32_t ( there 
is a bug report for this ), and this means trying to compile Boost 
libraries like type_traits without this patch yields many errors.

I would have used the BOOST_WORKAROUND macro but clang does not support 
a value which gives a single number for the compiler version so I felt 
that drumming up multiple BOOST_WORKAROUNDs using major/minor/patch 
version numbers was too much of a hack to bother about.