meson: Add some compiler arguments to debug builds

Just as Mutter does

GNOME/gnome-shell!464
4 jobs for !464 with debug-builds in 9 minutes and 43 seconds (queued for 1 second)
detached
Status Job ID Name Coverage
  Review
passed #247789
check_commit_log

00:05:14

 
  Build
passed #247790
build

00:02:41

 
  Test
passed #247791
test

00:01:46

passed #247792
test-pot

00:01:47