contrib: Do not pass debug/optim flags to meson

This fixes the meson underscore prefix test, which misbehaves when -g is passed, as it would detect the debug string without underscore first and incorrectly report that no underscore prefix for symbols is used.

Fixes build issues with dav1d, which relies on the underscore prefix check.

See: https://github.com/mesonbuild/meson/issues/5482 Signed-off-by: Hugo Beauzée-Luyssen hugo@beauzee.fr (cherry picked from commit 3426d7bcf98fee15c239ea2b3d815c613df82efe) Signed-off-by: Hugo Beauzée-Luyssen hugo@beauzee.fr