Fix `vercmp` warning in `pacman-packages`

[dscho]

The pacman-packages job shows warnings like these when adding new packages to the Pacman database:

==> Adding package 'mingw-w64-i686-git-2.48.0.rc1.windows.1-1-any.pkg.tar.xz'
D:/a/_temp/build-extra/repo-add: line 254: vercmp: command not found
D:/a/_temp/build-extra/repo-add: line 254: ((: > 0 : syntax error: operand expected (error token is "> 0 ")
  -> Computing checksums...
  -> Removing existing entry 'mingw-w64-i686-git-2.48.0.rc0.windows.1-1'...
  -> Creating 'desc' db entry...
  -> Creating 'files' db entry...

While they seem not to prevent the package from being added as intended, they are ugly and the underlying issue may cause future breakages.

Most likely the correct fix will be to add /usr/bin/vercmp.exe to the makepkg-git sparse-checkout definition.

The same will most likely need to be done for git-sdk-32 and git-sdk-arm64, too.