libctf compilation failure on MinGW

[Nick Alcock]

On 2 Jul 2020, Eli Zaretskii outgrape:

> We had a conversation about this back in February, AFAIR, and your
> conclusion was that you'd like to remove those E* constants from the
> sources, and thus avoid the problem altogether.
>
> Did you have time to make those changes since then?

I... tried. It's *so annoying* to use that I'm going to go for your
original approach, and just #define undefined-on-some-platform E*
constants as needed. (Maybe I should automate this, and scan *all* E*
constants used by libctf in configure and define suitable replacements,
to avoid the whack-a-mole nature of this?)

> GDB is about to branch for the imminent GDB 10.1 release, and
> currently the problems I described back then are still with us.

Oh, I thought you pushed a fix already! Sorry!

I'll post a fix sticking suitable E* #defines in once I get back from
holiday on Tuesday.

> we'd like a solution soon, and need to decide whether to go with the
> same workaround we used for GDB 9.1 or use a better change from you.

I think that workaround is in hindsight better than the change I
proposed, and should go in trunk. :/