new-build ignores --builddir option

[DanielG]

cabal new-build doesn't seem to respect --builddir, regardless of what I pass it still creates the dist-newstyle directory.

This is with HEAD (2146ea1).

As far as I can tell this is because DestDirLayout is constructed without considering any of the *DistPref fields from CliConfigFlags.

See

cabal/cabal-install/Distribution/Client/ProjectOrchestration.hs

Line 176 in 2502ea1

let distDirLayout = defaultDistDirLayout projectRootDir

I wouldn't mind submitting a PR for this if anyone can point out a good way to do this since I'm still new to the new-build code.

[ezyang]

See also #4124