Many -Wdeprecated-variadic-comma-omission warnings in preprocessed files in C++26

[Romain-Geissler-1A]

Hi,

When trying to use Boost.Proto (indirectly, through Boost.Xpressive), using gcc 15, C++ 26, and flags -Wall -Wextra -Werror we do get many -Wdeprecated-variadic-comma-omission warnings in preprocessed files (and possibly also in other files, I didn't check).

Here is the first warning I get:

/data/mwrep/res/osp/Boost/25-0-0-0/include/boost/proto/transform/detail/preprocessed/call.hpp:12:23: error: omission of ',' before varargs '...' is deprecated in C++26 [-Werror=deprecated-variadic-comma-omission]
   12 |     struct call<Fun(A0...)> : transform<call<Fun(A0...)> >
      |                       ^~~
      |

This is probably easily fixable by updating the wave rules to generate these, files, but I have honestly no idea how to even use this Boost.Wave thing (and I am not sure these preprocessing still make much sense in a post C++11 era) ;)