cc-options do not get passed to GHC

[bitonic]

cc-options currently do not get seem to get passed to GHC. It would be useful if they were, since GHC is capable of compiling C/C++ files and now it might more than before given the addition of addForeignFile in GHC 8.2, which lets users compile and link C/C++ files from TH.

[bitonic]

Note that in practice one needs to put the cc options both in cc-options and in ghc-options via -optc, since inline-c is often used with hsc2hs which does get the flags from cc-options.

[bitonic]

Note that the same happens for linking: extra-libraries are not passed to GHC, which makes loadDLL fail when it dlopens shared libraries referring to any of the specified extra-libraries.

[bitonic]

Note that cabal even emits warnings like

Warning: Instead of 'ghc-options: -lceres ...' use 'extra-libraries:
ceres ...'

even if they do not have the same effect.

[ezyang]

Related issue #3700

Not passing extra-libraries to GHC as -l is probably a separate bug. If this doesn't cause any regressions, we probably should do this, at the very least when other-extensions: TemplateHaskell is specified, and maybe unconditionally.

[ezyang]

@bitonic If you're interested in solving this ticket I'd be happy to advise.