Dear Maintainer,

To reproduce:
- install ccache
- $ export PATH=/usr/lib/ccache:$PATH
- get a haskell package sources and install its build-deps
- build it with dpkg-buildpackage

Attached log is haskell-skein build (after s/-v2/-v3/ in
/usr/share/cdbs/1/class/hlibrary.mk to make it more verbose).

I see HOME is set by ghc d/rules to /homedoesnotexistatbuildtime.
http://sources.debian.net/src/ghc/7.8.20140411-5/debian/rules#L17

How about setting it only if not already set? (not tested)

Thanks.