[feature request] Something like Make's --dry

[osa1]

It seems like current hsbencher doesn't have something like this(also confirmed in a private communication).

It's useful for scenarios like this:

• I have a hsbencher project with lots of sub-projects.
• Project is old, so none of the sub-projects build by default. I need to tweak .cabal files. (normally I just use --allow-newer but there's no way to tell hsbencher that)
• Since I can't know which projects hsbencher will be building, I need to run it and see how it's failing.
• After fixing that project, I need to loop and see how hsbencher is failing now.

With --dry, I'd just run ./benchmark --dry and see what it's going to build, and fix all of them at once.

[rrnewton]

FYI there should be some way to add "--allow-newer" to COMPILE_FLAGS so that it gets passed thrugh to the cabal install command for a cabal-built benchmark. Feel free to make this better documented or more discoverable if you see how.