C++ compiler check: use library

[Scott McPeak]

autoconf 2.53 uses the following program to test whether the C++ compiler
"works":

int
main ()
{

  ;
  return 0;
}

Since this program doesn't use the C++ standard library, it doesn't test
whether that library is correctly installed.

I get about one report a month from someone who has trouble with my
deployed software because the C++ standard library isn't installed
correctly on Solaris (by default gcc-2.95.x puts the library in
/usr/local/lib, but Solaris' ld.so doesn't look in /usr/local/lib).
(It's in my FAQ but of course not everyone reads it.)

For the next release of my software I'm going to add a test which tries to
compile and run a simple hello-world that uses cout.  However, I think the
autoconf-supplied test program ought to do that too, since my experience
is misconfigured libraries are a problem.

-Scott