Changes build_command to work with ghc-mod version 5

ghc-mod version 5 requires the command to be of the form:

    ghc-mod {command} -g {ghcOpt} {commandArgs}

for example:

    ghc-mod check -g -fno-warn-unused-binds path/to/File.hs ModuleName 1 2

In previous versions, the -g could be put right after ghc-mod (as ghcmod-vim does currently), or sometimes at the end of the whole thing, or other places; it was quite flexible. Now, the -g absolutely has to be in that position (which may be an error on the part of ghc-mod, but in any event is the behavior of current releases of version 5.*).

`ghcmod_build_make` is the only thing I was unsure of, and I wasn't able to run the tests so I'm not sure if the changes I did to them are working, but this is a step in the right direction at least.