VS: Fix support for v142 toolset minor versions in VS 16.5+

The fix in commit 5117389931 (VS: Fix support for v142 toolset minor
versions, 2019-10-01, v3.15.5~6^2) worked around a bug in VS's placement
of toolset files.   VS 16.5 will fix that bug and restore the original
pattern for locations of toolset files.  Update our logic to look for
both possibilities.

Issue: #19779
2 files changed