Test Plan:
```
ghci> import GHC.Stack
ghci> SrcLoc "f" "b" "c" 1 2 3 4
SrcLoc {srcLocPackage = "f", srcLocModule = "b", srcLocFile = "c",
srcLocStartLine = 1, srcLocStartCol = 2, srcLocEndLine = 3,
srcLocEndCol = 4}
```

Reviewers: austin, hvr, bgamari

Reviewed By: bgamari

Subscribers: thomie

Projects: #ghc

Differential Revision: https://phabricator.haskell.org/D1886

GHC Trac Issues: #11510