cabal: add "-hidir $TMPDIR" parameter to ghc call that compiles Setup.hs

Packages that don't have a Setup.hs file get to use a default version that
lives in the Nix store. By default ghc tries to put the Setup.o and Setup.hi
files in the same directory as the source file, which isn't writable. This
leads to build errors [1]. Thus, we re-direct those paths to a build-local
writable location: $TMPDIR.

Arguably, we could also use "." or copy the /nix/store/deadbeef-Setup.hs file
into the local source directory before compiling, which would work fine, too.

[1] https://github.com/NixOS/nixpkgs/issues/4851

pkgs/build-support/cabal/default.nix

@@ -194,7 +194,7 @@ assert !enableStaticLibraries -> versionOlder "7.7" ghc.version;
               for i in Setup.hs Setup.lhs ${defaultSetupHs}; do
                 test -f $i && break
               done
-              ghc --make -o Setup -odir $TMPDIR $i
+              ghc --make -o Setup -odir $TMPDIR -hidir $TMPDIR $i
 
               for p in $extraBuildInputs $propagatedNativeBuildInputs; do
                 if [ -d "$p/lib/ghc-${ghc.ghc.version}/package.conf.d" ]; then