Another workaround for GHC linking error "unknown symbol"

This error appears after adding the dependency to lifted-base.
See also #683 and ee7caf27.

I surmise that something like this is happening: Some code, that uses
the library, is only referenced through Template Haskell. A probable bug
in GHC linker fails to notice it and doesn't include the library when
linking, causing the error. Referencing the library explicitly in THH.hs
solves the problem.
Signed-off-by: Petr Pudlak <pudlak@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>

src/Ganeti/THH.hs

@@ -73,6 +73,7 @@ module Ganeti.THH ( declareSADT
 import Control.Arrow ((&&&))
 import Control.Applicative
 import Control.Monad
+import Control.Monad.Base () -- Needed to prevent spurious GHC linking errors.
 import Data.Attoparsec () -- Needed to prevent spurious GHC 7.4 linking errors.
   -- See issue #683 and https://ghc.haskell.org/trac/ghc/ticket/4899
 import Data.Char