Moritz Angermann authored Sep 06, 2017 and John Ericson committed Oct 03, 2018

The LLVM backend shells out to LLVMs `opt` and `llc` tools. This clean
up introduces a shared data structure to carry the arguments we pass to
each tool so that corresponding flags are next to each other. It drops
the hard coded data layouts in favor of using `-mtriple` and have LLVM
infer them. Furthermore we add `clang` as a proper tool, so we don't
rely on assuming that `clang` is called `clang` on the `PATH` when using
`clang` as the assembler.  Finally this diff also changes the type of
`optLevel` from `Int` to `Word`, as we do not have negative optimization
levels.

Reviewers: erikd, hvr, austin, rwbarton, bgamari, kavon

Reviewed By: kavon

Subscribers: michalt, Ericson2314, ryantrinkle, dfeuer, carter, simonpj,
kavon, simonmar, thomie, erikd, snowleopard

Differential Revision: https://phabricator.haskell.org/D3352

(cherry picked from commit 22733532)