Workaround "Pattern match has inaccessible right hand side" bug (#2611)

When using GHC < 9 .../ICE40/Blackboxes/IO.hs sometimes(?) warns:
    Pattern match has inaccessible right hand side
    In a pattern binding in
         a pattern guard for
           an equation for ‘sbioTemplate’:
        [_HasCallStack,
         (clk, clkTy, _),
         (en, _enTy, _),
         (pinConfig, _pinTy, pinConfigLiteral -> ()),
         (packagePin, packagePinTy, _),
         (latchInput, Bit, _),
         (dOut0, Bit, _),
         (dOut1, Bit, _),
         (outputEnable, Bool, _)]
        <-
        ...
And because we run with -Werror on CI this causes compilation to fail.
This works around that by explicitly turning it back into a warning.

Author: leonschoorl

clash-cores/src/Clash/Cores/LatticeSemi/ICE40/Blackboxes/IO.hs

@@ -5,11 +5,19 @@
 
   HDL generation functionality for LATTICE ICE IO primitives.
 -}
+
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE ViewPatterns #-}
 
 {-# OPTIONS_HADDOCK hide #-}
 
+-- GHC < 9, sometimes(?) compains about the RHS of sbioTemplate being unreacheble,
+-- this explicitly turns that into an warning overriding -Werror.
+#if __GLASGOW_HASKELL__ < 900
+{-# OPTIONS_GHC -Wwarn=overlapping-patterns #-}
+#endif
+
 module Clash.Cores.LatticeSemi.ICE40.Blackboxes.IO (sbioTF) where
 
 import           Prelude