cmake - add option for fixed point debug

Signed-off-by: Ralph Giles <giles@thaumas.net>
3 jobs for master in 4 minutes and 59 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed autoconf #10978
docker

00:04:59

passed cmake #10979
docker

00:02:02

passed meson #10980
docker

00:02:32