bpo-31569: globally fix case for PCbuild where it was PCBuild

[gronke]

While setting up the development environment for Windows I've noticed PCbuild/ was sometimes written with a different case. This pull-requests replaces all occasions of PCBuild with PCbuild.

https://bugs.python.org/issue31569

[serhiy-storchaka]

Please open an issue on the bug tracker for discussing your changes.

File systems on Windows are case-insensitive. It is not clear what is the canonical name of PCbuild. Wouldn't be easier to make a replace in the reverse direction?

[gronke]

File systems on Windows are case-insensitive. It is not clear what is the canonical name of PCbuild. Wouldn't be easier to make a replace in the reverse direction?

The directory was called PCbuild since 2.7, so I guess PCBuild is a typo that was never noticed because it was never an issue on case-insensitive filesystems.

[josephshen]

this bug happened and I think it's need port back to all affected version.
it happens when try to compile on on a VM's mapped host filesystem ( e.g. host macOS with case-sensetive filesystem and client Windows)