The fix in commit 51173899 (VS: Fix support for v142 toolset minor
versions, 2019-10-01, v3.16.0-rc1~32^2) 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