ghc-7.10 and earlier build with minimal changes, but are not supported

[kvanbere]

Can be seen here:
rahulmutt@cf16054

@rahulmutt feel free to add a gate on the options needed for this to build and submit your fork as a pull request.

[kvanbere]

see also tsani/servant-github-webhook#11 .

[rahulmutt]

@donkeybonks Spent some time looking at the blame for the new warning flags and I found this:
ghc/ghc@2206fa8

So essentially, -Wincomplete-uni-patterns -Wincomplete-record-updates can be replaced with -fwarn-incomplete-uni-patterns -fwarn-incomplete-record-updates to make it work for older GHC versions too. According to the commit comment:

The old -fwarn...-based warning flags will remain functional for the forseeable future.

So I think doing s/-W/-fwarn-/ is a safe option that keeps everyone happy. I don't think you should go with my forked changes since I did those in a rush and didn't check to see if there were any alternatives.