Templatized C++ Command Line Parser

'Treat wchar_t as Built-In type' set to 'No' (/Zc:wchar_t-) causes a build
failure because of the duplicate template specialization caused by wchar_t
being typedef-ed as a unsigned short.

The full error is:

tclap-1.2.0\include\tclap\StandardTraits.h(175) : error C2766: explicit
specialization; 'TCLAP::ArgTraits<unsigned short>' has already been
defined
tclap-1.2.0\include\tclap\StandardTraits.h(106) : see previous
definition of 'ArgTraits<unsigned short>'

The solution I came up with is to not declare the specialization if the
compiler is MSVC and if wchar_t is not defined as a native type, something
like this:

#ifdef _MSC_VER
#ifndef _NATIVE_WCHAR_T_DEFINED
#define TCLAP_DONT_DECLARE_WCHAR_T_ARGTRAITS
#endif
#endif

Then do something like this in StandardTraits.h:

#ifndef TCLAP_DONT_DECLARE_WCHAR_T_ARGTRAITS

template<>
struct ArgTraits<wchar_t> {
typedef ValueLike ValueCategory;
};

#endif