[Bug c++/127218] [13/14/15/16/17 Regression] constexpr memchr/strchr/strrchr/strstr count a nonzero offset in the first argument twice

[stevensudit at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127218

--- Comment #1 from Steve Sudit <stevensudit at gmail dot com> ---
Created attachment 65502
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=65502&action=edit
Proposed fix with testsuite addition