Fix bug in preprocessing test suites and benchmarks

Preprocessed files would be written to dist/build instead of
dist/build/my-test-suite/my-test-suite-tmp, causing them not to be
found during compilation.

Fixes #1087.

Cabal/Distribution/Simple/PreProcess.hs

@@ -232,7 +232,7 @@ preprocessComponent pd comp lbi isSrcDist verbosity handlers = case comp of
     preProcessComponent bi modules exePath dir = do
         let biHandlers = localHandlers bi
             sourceDirs = hsSourceDirs bi ++ [ autogenModulesDir lbi ]
-        sequence_ [ preprocessFile sourceDirs (buildDir lbi) isSrcDist
+        sequence_ [ preprocessFile sourceDirs dir isSrcDist
                 (ModuleName.toFilePath modu) verbosity builtinSuffixes
                 biHandlers
                 | modu <- modules ]