Can't build happy with ghc 7.2.1

[David Fox <ddssff@gmail.com>]

I patched the ghc in experimental so it was 7.2.1, but I can't build
the happy deb with it.  It gets to "Preprocessing executable 'happy'
for happy-1.18.6..." and then dies with exit code 127.  This was using
an Ubuntu Natty build environment.