I just came across this same issue, and would like to request adding Win32 as platform name, in favour of the current x86.
Now I could add a appveyor.yml file to my repository, but I'd rather not, because I am working on a fork and don't want that file to be part of my pull-requests, and/or history.
Is there a known workaround? This is what I came up with so far:
if "%platform%"=="x86" set platform=Win32
This way, the actual build succeeds; sadly right after the last project finishes compiling, I get this line in teh build log:
Project configuration not found: Project=ALL_BUILD, Configuration=Debug, Platform=x86.
What triggers it? Is there another Pre-Something script where I could add my workaround?