Improve response file support

The response file support in base is missing a few details when compared with for example GNU's libiberty. For example, base's implementation errors on missing files, and does not support recursive response files.

Since the solution implemented in Cabal's Distribution.Compat.ResponseFile module uses functions from System.FilePath, I can't directly upstream those changes.

A potential solution is moving GHC.ResponseFile to a package other than base, so I'm raising this issue to discuss that or other ideas.

GNU implementation: http://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=libiberty/argv.c;h=6444896f995a8e4abfb6a1edc510f3a4bbe1a30b;hb=HEAD#l342
Cabal motivation: https://github.com/haskell/cabal/issues/6061
Cabal changes: https://github.com/haskell/cabal/pull/6063

Itemised improvements:

1. Missing files should be passed as literal arguments
2. Response files should be recursively expanded, with a limit (requires something like System.FilePath(takeDirectory, (</>)) for expansions relative to each response file)
3. libiberty errors if an @... argument is found, but is a directory