standards/175811: libstdc++ needs complex support in order use C99

[Garrett Wollman]

<<On Thu, 30 May 2013 07:56:24 -0600, Warner Losh <imp at bsdimp.com> said:

> I'm all for getting everything we can into the tree that produces an
> answer that's not perfect, but close. What's the error that would be
> generated with the naive implementation of

> long double tgammal(long double f) { return tgamma(f); }

Perhaps we could implement these functions in such a way that they
logged a message to inform the user (once per process) that they were
using a low-quality implementation.  That would allow us to implement
these functions without totally losing the incentive to implement them
properly, and those users who don't actually call those functions
would not have to pay the price of further delay.  (This would be a
non-conforming implementation, since it would have side effects other
than those specified by the standard, but we already fail to conform
by not implementing the functions at all, so it wouldn't make things
*worse*.)

-GAWollman