[Patch] Fix ac_c99_complex configury

[Ian Lance Taylor]

Mark Mitchell <mark@codesourcery.com> writes:

> >>>You can't use any link tests in this macro, it's used by crosses and
> >>>native toolchains.
> >>
> >>I thought you just couldn't use run tests.  Why can't you use link tests?
> > At least this is not *totally* obvious, fiuu! Thanks: often I feel a
> > little stupid when I have to do with the configury bits and now I can
> > fool myself that I'm not more naive than our release manager, great! ;) ;)
> 
> Heh.  Do you actually know the answer to my question, or are you
> confused like me?

Doing link tests normally requires startup files.  Historically, when
building a cross-compiler, the startup files may or may not be
available when building libstdc++.  If the target uses libgloss, the
startup files are probably available, depending upon how the build is
done.  If the person building the tools has gone to the effort of
putting the startup files in, e.g., $(tooldir)/lib, then they are
available.  But otherwise they are not available.

In general it is convenient to be able to be able to build the
compiler itself without requiring the toolchain to be fully set up
beforehand.  This is particularly true when doing a Canadian Cross.
That is why, historically, we have required that the target library
configurations not require link tests.  If you look at the libiberty
configure script, for example, you will see that it goes to
considerable lengths to avoid doing link tests in a cross
configuration.

We could change that decision.  For all I know, we have already
changed that decision accidentally.  But I think it would be a change,
and it would raise another barrier in the already high barriers for
the non-cognoscenti to build a cross toolchain.

Ian