pyoxidizer: pass arch to WiXInstaller() We just upgraded Windows automation to PyOxidizer 0.17.0. This version of PyOxidizer changed the behavior of WiX installers so installer architecture defaulted to "x64" (before it defaulted to the target of the pyoxidizer.exe binary). To allow controlling the architecture of the installer, the `arch` argument was added to `WiXInstaller`. This commit passes that argument in. Differential Revision: https://phab.mercurial-scm.org/D11358