meson.build: re-add -fno-omit-frame-pointer for easier debugging
meson.build: re-add -fno-omit-frame-pointer for easier debugging

This got lost in commit 2f5410a71fceeb4aa168560cdbd624f5fab29262
(Meson migration), and today with Dwarf support it is mostly useless,
but sometimes it is still necessary when debug tools are broken and
Dwarf doesn't work.

CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy