[Bug other/116951] Use -D_GLIBCXX_ASSERTIONS for --enable-checking=yes

[sjames at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116951

--- Comment #1 from Sam James <sjames at gcc dot gnu.org> ---
=extra would work for me as well if we really don't want to put it in 'yes'.