This fixes warnings following
    commit 910a642294eb3547d0cbb3d5735ad81b964f137b
    Author: Simon Peyton Jones <simonpj@microsoft.com>
    Date:   Mon Oct 29 23:25:25 2012 +0000
    Do not treat a constructor in a *pattern* as a *use* of that constructor

I'm not sure if this is the right thing to do: In
    commit 1c4608e3
    Author: Simon Marlow <marlowsd@gmail.com>
    Date:   Thu Feb 19 10:05:32 2009 +0000
    Rewrite of signal-handling.
the commit message says:
    The new implementation has the capability to define signal handlers
    that have access to the siginfo of the signal (#592), but this
    functionality is not exposed in this patch.
but this at least gets validate builds working again, and we can change
it if necessary as part of #2451