Update project to MSVC 2013 tools

Retaining XP support, using SDK 7.1a (v120_xp.)  Disables SSE2 flag on x64 since it's implied and causes compile warnings.

If merged, hrydgard/ppsspp#5371 will need to be merged too or PPSSPP won't compile anymore.  May affect other (non-PPSSPP) projects in the same way.

-[Unknown]