GHC 7.4.2 on Ubuntu Trusty

[Edward Z. Yang]

Excerpts from Yitzchak Gale's message of 2014-10-28 13:58:08 -0700:
> How about this: Currently, every GHC source distribution
> requires no later than its own version of GHC for bootstrapping.
> Going backwards, that chops up the sequence of GHC versions
> into tiny incompatible pieces - there is no way to start with a
> working GHC and work backwards to an older version by compiling
> successively older GHC sources.
> 
> If instead each GHC could be compiled using at least one
> subsequent version, the chain would not be broken. I.e.,
> always provide a compatibility flag or some other reasonably
> simple mechanism that would enable the current GHC to
> compile the source code of at least the last previous released
> version.

Here is an alternate proposal: when we make a new major version release,
we should also make a minor version release of the previous series, which
is prepped so that it can compile from the new major version.  If it
is the case that one version of the compiler can compile any other
version in the same series, this would be sufficient to go backwards.

Concretely, the action plan is very simple too: take 7.6 and apply as
many patches as is necessary to make it compile from 7.8, and cut
a release with those patches.

Edward