Fix build.ps1 argument handling

Regressed with https://github.com/dotnet/msbuild/commit/9b7c97b8b10554deafe3fe9794d7eea9847b85d3

Some of the arguments that aren't defined as params in the eng/build.ps1 scripts but are available in Arcade's eng/common/build.ps1 script can't be used if other defined params exist with the same shortcut, i.e. `-build` because another param starting with a `b` is defined.