add _HAVE_LONG_DOUBLE flag, math.h update

[Jeff Johnston]

Howland Craig D (Craig) wrote:
> Jeff and I had some off-list discussions about this.  The end result is
> that the fixed-number method (e.g. #define NAN (0.0F/0.0F)) is the
> only one that works correctly in all situations when the 3.3 and later
> GCC builtins are not used in math.h.  No warnings are produced for old
> GCC versions that use them (at least not 3.2.3 and 2.95, which I have
> to test with).
>  
> g++ would warn for the divide-by-0 in the NAN definition, so a
> workaround
> to avoid such warnings is added for GCC C++.  This method errors out
> with plain gcc, which is why it is a special case for only g++.
>  
> Other than the tweak in the math.h changes, the other file changes in
> the
> patch are identical to the prior patches.
>  
> Craig
>   
Patch applied with Makefile.in regenerated as well.

Thanks,

-- Jeff J.