share more build options between targets

tahoe-ssk.cabal

@@ -60,7 +60,20 @@ extra-source-files: test/data/*
 common warnings
   ghc-options: -Wall
 
+common language
+  default-extensions:
+    DerivingStrategies
+    GeneralizedNewtypeDeriving
+    NamedFieldPuns
+    OverloadedStrings
+    PackageImports
+    RecordWildCards
+
+  default-language:   Haskell2010
+
 library
+  import:          warnings
+  import:          language
   hs-source-dirs:  src
   exposed-modules:
     Tahoe.SDMF
@@ -87,20 +100,11 @@ library
   -- This dependency isn't ideal.  Move common bits out to
   -- another library.
   build-depends:   tahoe-chk
-  ghc-options:        -Wall
-  default-extensions:
-    DerivingStrategies
-    GeneralizedNewtypeDeriving
-    NamedFieldPuns
-    OverloadedStrings
-    PackageImports
-    RecordWildCards
-
-  default-language:   Haskell2010
 
 test-suite tahoe-ssk-test
   -- Import common warning flags.
   import:             warnings
+  import:             language
 
   -- Base language which the package is written in.
   default-language:   Haskell2010