[Patch] Fix ac_c99_complex configury

[Gabriel Dos Reis]

Paolo Carlini <pcarlini@suse.de> writes:

| > I'm sure some our customers are still using <iostream.h>...  It's not
| > a terribly hard thing to change, but it can mean updating all of your
| > (thousands of) source files.  I don't have an opinion on whether V3
| > should rip this out or not.
| 
| Same here, I don't have a strong opinion. Certainly would simplify
| solving the problem at issue and certainly we deprecated it already for
| *3.3*.

yes, but I'm afraid that is insufficient.  My opinion is that we would
have to carry that baggage for a decade at least.

-- Gaby