Make sure preprocessed module are on the module path

test/data/cabal-preprocessors/Main.hs

@@ -0,0 +1,4 @@
+import Preprocessed
+
+main :: IO ()
+main = return warning

test/data/cabal-preprocessors/Preprocessed.hsc

@@ -0,0 +1,3 @@
+module Preprocessed where
+
+warning = ()

test/data/cabal-preprocessors/cabal-preprocessors.cabal

@@ -0,0 +1,14 @@
+name:                cabal-preprocessors
+version:             0.1.0.0
+license-file:        LICENSE
+author:              asd
+maintainer:          asd
+build-type:          Simple
+cabal-version:       >=1.10
+
+executable cabal-preprocessors
+  main-is:             Main.hs
+  build-depends:       base
+  default-language:    Haskell2010
+  other-modules:       Preprocessed
+  ghc-options:         -Wall