Revert r234649 "PECOFF: Use C++11 braced init list to make Version objects."

This doesn't compile with MSVC 2013:
include\lld/ReaderWriter/PECOFFLinkingContext.h(356) : error C2797:
    'lld::PECOFFLinkingContext::_imageVersion': list initialization
    inside member initializer list or non-static data member initializer
    is not implemented
include\lld/ReaderWriter/PECOFFLinkingContext.h(357) : error C2797:
    'lld::PECOFFLinkingContext::_imageVersion': list initialization
    inside member initializer list or non-static data member initializer
    is not implemented

llvm-svn: 234676