GHC-generated LINE annotation might cause non-deterministic build

[AlexWrapper-basic copy.txt](https://github.com/simonmar/alex/files/1003043/AlexWrapper-basic.copy.txt)

theres thousands of newlines in that attached file!
also some of the source / line attributions seem likely to cause nondeterminstic builds under some conditions
eg
```

{-# LINE 1 "/var/folders/py/wgp_hj9d2rl3cx48yym_ynj00000gn/T/ghc64947_0/ghc_2.h" #-}
```

cc @hvr

Start by examining the attached AlexWrapper-basic.copy.txt and the generated source around the GHC LINE annotation shown in the issue. Reproduce the generation process and determine whether temporary paths or excess newlines vary between builds; done means generated output is deterministic under the affected conditions.

Written by the indexing model from the issue text.