Only run benchmarks specified as build targets

[mgsloan]

Currently which benchmark targets are selected is ignored when actually running them - see this FIXME. Should be as simple as providing the benchmarks as component parameters here, and testing that it works properly.

[rvion]

link above in description is broken, correct url is : https://github.com/commercialhaskell/stack/blob/master/src/Stack/Build/Execute.hs#L1281

[mgsloan]

Ah, yes, fixed. That's what I get for using unpushed SHAs! (I've got an emacs keybinding that creates a github url based on the current SHA + line)