Support .buildinfo files in stack ghci.

[mboes]

Distribution.Simple based Setup.hs sometimes create
<package>.buildinfo files as an artifact of the configure phase.
This is the case in particular when using the autoconf hooks. Since
this is an internal detail private to any given package's Setup.hs,
Stack shouldn't (and doesn't) need to care or be aware of this. But
stack ghci does, since in that use case we're not using Cabal to
build - we're taking care of the build ourselves. In particular,
ignoring the <package.buildinfo file can mean that a successful
build using stack build can't be replicated using stack ghci.

E.g. in the case of the network package, the set of C files to build
is decided at configure time, based on the current platform. So the
c-files stanza in the .cabal file is not complete. This in turn
means stack ghci isn't aware of all object files it has to link in,
leading to obscure link errors (see #1239).

See 1 for more on .buildinfo files.

Fixes #2239.

To test:

$ stack unpack network
$ cd network
$ stack ghci

Without this patch the above sequence of commands doesn't work.

[mgsloan]

Cool, resolving this'd make a lot of people happy, I didn't realize it'd be so simple.

Are there any possible interactions between buildinfo files and Cabal versions? Like if stack updates to building against Cabal-1.24, will it read buildinfo files from Cabal-1.18?

In other words, unlike cabal-install, the Cabal that stack is built against can vary with the one that's used for building.

[mboes]

This patch doesn't depend on any new Cabal modules that Stack didn't depend on previously. The only new function it depends on is readHookedInfo and updatePackageDescription, both of which are part of Cabal-the-library (and I think mandated by Cabal-the-spec, though I haven't checked). The .buildinfo files are just text files that are meant to contain a subset of the syntax for .cabal files. It's up to the user to make sure (s)he writes both .cabal and .buildinfo files in a given project in a way that is compatible with the Cabal version that Stack uses.