safe-0.3.21 fails to build with GHC 7.10

[RyanGlScott]

As seen in this failing CI job, safe-0.3.21 fails to build with GHC 7.10.3:

Failed to build safe-0.3.21.
Build log ( /github/home/.cabal/logs/ghc-7.10.3/safe-0.3.21-778d784b35fd9e4ac1f942681fe8cd099de3d419b7f2923fa9feb12f55f4e0b4.log ):
Configuring library for safe-0.3.21..
Preprocessing library for safe-0.3.21..
Building library for safe-0.3.21..

Safe.hs:4:16:
    unknown flag in  {-# OPTIONS_GHC #-} pragma: -Wno-x-partial

Safe.hs:4:16:
    unknown flag in  {-# OPTIONS_GHC #-} pragma: -Wno-unrecognised-warning-flags
Error: cabal-3.10.1.0: Failed to build safe-0.3.21 (which is required by singletons-2.1). See the build log above for details.

This is because GHC 7.10 and earlier only support warning flags in the style of -fwarn-* and -fno-warn-*. The -W* and -Wno-* style of warning flags weren't introduced until GHC 8.0.

Would you be willing to raise safe's lower version bounds on base to >= 4.9 to exclude it from being buildable with GHC 7.10?

[ndmitchell]

Thanks for letting me know. Done on master, and also made a revision on Hackage to the 0.3.21 release.