Support x86_64 builds on aarch64 Windows

[gaborcsardi]

Installation fails because rig uses Program Files\R-aarch64 instead of Program Files (x86)\R. The installer actually succeeds, rig fails to patch the installation afterwards. It also does not know about installed x86_64 versions at all:

PS F:\works\rig> rig add 4.5.0 --arch x86_64
▶ Cleaning leftover registry entries
▶ Downloading https://cran.rstudio.com/bin/windows/base/old/4.5.0/R-4.5.0-win.exe -> C:\Users\GABORC~1\AppData\Local\Temp\rig\x86_64-R-4.5.0-win.exe
▶ Installing C:\Users\GABORC~1\AppData\Local\Temp\rig\x86_64-R-4.5.0-win.exe
⚠ Corrupt R profile at C:\Program Files\R-aarch64/R-4.6.0\library\base\R\Rprofile, try reinstalling R. If the issue perists, report it to rig developers.
▶ Installing pak for R 4.6.0 (if not installed yet)
PS F:\works\rig> rig ls 
* name   version    aliases
------------------------------------------
  4.5.2             
  4.5.3             
* 4.6.0             release
  devel  (R 4.7.0)  
PS F:\works\rig>