GNUtoMS: Add support for VS 2013 (#14936)

Add to the Platform/Windows-GNU module list of VS registry entries those
for VS 2013.  Also add the name "vcvars64.bat" used by VS 10 and above
for 64-bit tools.
Merge topic 'GNUtoMS-vs-12' into next

668e571d GNUtoMS: Add support for VS 2013 (#14936)