complex support on solaris?

[Greg Troxel]

As pkgsrc maintainer of the guile package, I got a bug report about not
building on Solaris.  The submitter doesn't have enough time for guile
any more, but the problem seems to be that Solaris's
/usr/include/complex.h expects the "compilation environment" to provide
_Complex_I.

Adding this line to numbers.c allowed it to build:

#define _Complex_I 1.0fi

The full PR is at:

  http://www.netbsd.org/cgi-bin/query-pr-single.pl?number=37556

So this seems to be a gcc/Solaris interaction where they don't jointly
meet C99.

On NetBSD-current, _Complex_I is provided in complex.h (gcc 4.1.3).

On NetBSD-4, complex.h is not provided at all (gcc 4.1.2).

So I wonder if guile should test for _Complex_I as well in the complex.h
case, and ignore complex.h if _Complex_I isn't defined.

(Separately gcc on Solaris should define it, probably, but I don't fully
understand the standard here.)