Emmanuele Bassi authored Sep 11, 2023 and Philip Withnall committed Jun 14, 2024

We have required C99 for a while; in the meantime, most C toolchains
have moved on to C11 or later as the default C standard.

We still allow for C99 toolchains, but in the future we are going to
require a C11 toolchain to build and use GLib.