[v3] Fix / clean-up config vs crosses (5/n): avoid a TRY_RUN

[Paolo Carlini]

Hi,
> Yes, breaking ABI compatibility is of course a major issue, so I
> wouldn't suggest doing that.  Obviously, run-time checks impose some
> overhead, but for future situations similar to this, it might be the
> best thing.  You have to open the file anyhow; if the open fails, then
> set a global variable and fall back to Plan B.  I would suspect that the
> cost would be pretty low.
>   
Agreed. In any case, we should consider that the problem with 
GLIBCXX_CHECK_RANDOM_TR1 impacts a minor, isolated, part of <tr1/random> 
(by itself, the implementation of a non-normative TR), I think the 
crosse-compilers people can live with this bit of incorrectness in the 
configury for a little more time.
> As for GCC_CHECK_UNWIND_GETIPINFO, that looks like something that could
> be a compile-time test (on all targets, whether or not native).  As
> discussed previously, it really *should* be a link-time test, but unless
> people are willing to rethink the one-tree build stuff, we're not
> allowed link-time tests.
>   
Ok, but then, let's ask the author of the test: Steve?
> And, as for AM_ICONV, unfortunately, I'm totally iconv-illiterate. :-(
>   
Sigh, two of us ;)

Paolo.