Re: Major issues with g++ 6 and gnulib

[Jonathan Wakely]

On 20/02/16 02:07 +0000, Jonathan Wakely wrote:
> The next problem is that gnulib defines:
>
> inline int signbit (float f) { return _gl_cxx_signbitf (f); } inline
> int signbit (double d) { return _gl_cxx_signbitd (d); } inline int
> signbit (long double l) { return _gl_cxx_signbitl (l); }
>
> GCC 6 provides a standard-conforming <math.h> which defines the same
> signbit overloads (as required by C++11 and C++14).  So the gnulib
> header is incompatible with any conforming C++11 implementation.
>  
Here's a patch for Octave which hacks around the above problem in
gnulib and then fixes Octave to include gnulib headers explicitly,
instead of assuming they'll get found by GCC's std::lib.

I haven't waited for octave to finish building (it's after 3am here)
but if other files fail just #include <libgnu/math.h> or #include
<libgnu/stdlib.h> and it should work.

The gnulib change is a hack, a proper fix would only skip the signbit
overloads for __cplusplus >= 201103L, but would also make sure to
#undef signbit if there's an earlier #define signbit 1. Maybe that
should be done by defining @GNULIB_SIGNBIT@ to something different.