Reply from Kim J. Nordmo @AdmiringWorm on the Chocolatey Gitter Channel.
@dhoer, as far as I know, there is no way to get all the arguments, just the arguments passed with --package-args.
However, if you only need to find out if the user is trying to force --x86, then you can check if the next environment variable is $env:chocolateyForceX86$ true
Example
if ((Get-ProcessorBits 32) -or $env:ChocolateyForceX86 -eq $true) {}