This PR adds a cmake option `WITH_WINDOWS_EXTERNAL_MANIFEST`
which is off by default which addresses the following 2 problems:
The CI env occasionally fails to link the manifest into blender.exe
with mt.exe getting file in use error. The solutions mentioned online
vary wildly between, just rebuild, turn off your AV, use this magic
switch. None of them actually point to a root cause we can address.
When building blender with clang and the visual studio generator
it also somehow doesn't embed the manifest.
If the bots stay problematic this option can be turned on for the CI
environment, and will be automatically turned on when it detects clang
and the visual studio generator being used.
Pull Request: https://projects.blender.org/blender/blender/pulls/111683
39c901407e