[patch] Update build flags for new compiler feature

[Eric Blake]

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According to Dave Korn on 10/2/2009 3:11 PM:
>   So, nobody did ask for a compiler version check(*), so here's the patch plus
> changelog, and I'd like to get separate OKs from both cgf and cv to say that
> you've each either updated your cross-build environments or don't mind
> patching the flag back out locally until you can.

I just noticed that the gcc-4 available on 1.5 is no longer sufficient to
do a self-hosted build of 1.7.  Not a show-stopper, since I have
successfully built self-hosted under 1.7 using the latest patch, but it
was kind of kind of convenient being able to build under 1.5, as it meant
fewer cygwin 1.7 processes to stop before installing a just-built dll.

- --
Don't work too hard, make some time for fun as well!

Eric Blake             ebb9@byu.net
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