GEODE-2467: Switch Xerces CMakeLists.txt to highest supported Visual Studio version.
GEODE-2467: Switch Xerces CMakeLists.txt to highest supported Visual Studio version.

- Also move MSVC_VERSION check above if (WIN32) check
- This change allows building Xerces with Visual Studio 2015 (called
14.0 internally).

This closes #7.

PivotalSarge/geode-native,mmartell/geode-native,mhansonp/geode-native,PivotalSarge/geode-native,pivotal-jbarrett/geode-native,PivotalSarge/geode-native,pivotal-jbarrett/geode-native,pivotal-jbarrett/geode-native,mmartell/geode-native,mhansonp/geode-native,mhansonp/geode-native,mmartell/geode-native,pivotal-jbarrett/geode-native,PivotalSarge/geode-native,mmartell/geode-native,mhansonp/geode-native,pivotal-jbarrett/geode-native,mmartell/geode-native,PivotalSarge/geode-native,PivotalSarge/geode-native,pivotal-jbarrett/geode-native,mhansonp/geode-native,pivotal-jbarrett/geode-native