[RFC] libstdc++/15361, or: remove or fix the SGI extensions in bitset??

[Paolo Carlini]

Hi,

the PR points out some problems (I'm almost sure the analysis is correct)
in 3.4.0 with the SGI extension bitset::_M_do_find_next.

However, before further studying the technical details of the PR, seems
appropriate deciding whether we really want to /keep/ that extension (and
_M_do_find_first) or not!

What do you think?

Paolo.