X.U.Grab: Hide mkGrabs from XMonad

With [1] merged, the XMonad module from core now exports mkGrabs and
setNumlockMask (now cacheNumlockMask).  However, since we want
xmonad-contrib 0.17.1 to compile against xmonad 0.17.0 still, hide the
function for now and continue to use the vendored copies we have in
X.U.Grab currently.  We have to ignore the dodgy-imports warning when
-fpedantic is on, but that seems like a small price to pay.

A breaking change for this is planned for 0.18.0.

[1]: xmonad/xmonad#405

XMonad/Util/Grab.hs

@@ -29,7 +29,7 @@ module XMonad.Util.Grab
   ) where
 
 -- core
-import           XMonad
+import           XMonad                         hiding (mkGrabs)
 
 import           Control.Monad                  ( when )
 import           Data.Bits                      ( setBit )

xmonad-contrib.cabal

@@ -76,7 +76,7 @@ library
     ghc-options:   -Wall -Wno-unused-do-bind
 
     if flag(pedantic)
-       ghc-options: -Werror -Wwarn=deprecations
+       ghc-options: -Werror -Wwarn=deprecations -Wwarn=dodgy-imports
 
     -- Keep this in sync with the oldest version in 'tested-with'
     if impl(ghc > 8.4.4)
@@ -478,7 +478,7 @@ test-suite tests
   default-language: Haskell2010
 
   if flag(pedantic)
-     ghc-options: -Werror -Wwarn=deprecations
+     ghc-options: -Werror -Wwarn=deprecations -Wwarn=dodgy-imports
 
   -- Keep this in sync with the oldest version in 'tested-with'
   if impl(ghc > 8.4.4)