Revert "Suppress non-conforming GNU paste extension in all standard-conforming modes"
    
    This reverts commit f4537935dcdbf390c863591cf556e76c3abab9c1.
    This reverts commit b43c26d036dcbf7a6881f39e4434cf059364022a.
    
    This GNU and MSVC extension turns out to be very popular. Most projects
    are not using C++20, so cannot use the new __VA_OPT__ feature to be
    standards conformant. The other workaround, using -std=gnu*, enables too
    many language extensions and isn't viable.
    
    Until there is a way for users to get the behavior provided by the
    `, ## __VA_ARGS__` extension in the -std=c++17 and earlier language
    modes, we need to revert this.
    
    (cherry picked from commit 61a66e4b5ec18e9e73c2f6334f6b7f7dd4bca77e)