linking problems with ghc-7.8 on linux about cuda

[tmcdonell]

@mchakravarty ghc bug?

[mchakravarty]

@tmcdonell May be a change in how GHC interprets the package info, but I'm not sure it is a GHC bug. Maybe we where just lucky that it used to work with the old GHC (as we arguably should have always put the C libraries into extra-libraries).

I guess, the culprit is

cuda_ldflags="$LDFLAGS $LIBS "

in configure.ac. The $LIBS need to go into a separate variable that is substituted into the extra-libraries.

[tmcdonell]

Ah, good catch.

I was thinking that it is probably simpler to do away with the configure script and just put the default library paths etc. into the cabal file, rather than trying to search for them based on the location of nvcc. This might also help the situation on windows.

[mchakravarty]

I don't think, this is going to work for OS X. We put quite a bit of extra stuff into the LD flags on that platform.

[mchakravarty]

(So, I'd suggest to only change the Linux setup conditionally to fix this.)