Issue #20966: Fix Tkinter Resources link
Ignore files generated by MSVC PGO builds.
Clean up PCbuild/pcbuild.sln a bit:

- Remove configuration settings from removed _sha3.vcxproj
- Don't try to build configurations of _testembed that don't exist
  (namely, PGInstrument and PGUpdate)
Avoid compile warning in xxlimited on 32-bit Windows non-Debug builds.