Add test for --working-dir and hsc2s

Before the previous patches this test failed because an incorrect path
was passed to hsc2hs (a preprocessor), it now succeeds :)

cabal-testsuite/PackageTests/WorkingDirRel/WD_NO_MENTION/CHANGELOG.md

@@ -0,0 +1,5 @@
+# Revision history for n
+
+## 0.1.0.0 -- YYYY-mm-dd
+
+* First version. Released on an unsuspecting world.

cabal-testsuite/PackageTests/WorkingDirRel/WD_NO_MENTION/app/Main.hsc

@@ -0,0 +1,3 @@
+module Main where
+
+main = print ()

cabal-testsuite/PackageTests/WorkingDirRel/WD_NO_MENTION/n.cabal

@@ -0,0 +1,19 @@
+cabal-version:   3.0
+name:            n
+version:         0.1.0.0
+license:         NONE
+author:          Matthew Pickering
+maintainer:      [email protected]
+build-type:      Simple
+extra-doc-files: CHANGELOG.md
+
+common warnings
+    ghc-options: -Wall
+
+executable n
+    import:           warnings
+    main-is:          Main.hs
+    build-depends:    base
+    hs-source-dirs:   app
+    build-tool-depends: hsc2hs:hsc2hs
+    default-language: Haskell2010

cabal-testsuite/PackageTests/WorkingDirRel/setup.test.hs

@@ -0,0 +1,4 @@
+import Test.Cabal.Prelude
+
+main = setupTest $ recordMode DoNotRecord $ do
+  withDirectory "WD_NO_MENTION" $ setup_build []