[PATCH] Makefile.global: drop -std=gnu99. C11 (or later) compiler required

[David Bremner]

Tomi Ollila <tomi.ollila at iki.fi> writes:

> Since October 2018 building notmuch has actually required compiler
> that knows C11.
>
> Also this -std=gnu99 was not used in code compiled by configure,
> so in theory this could have caused problems...
>

pushed.

d