Fix linking dav1d in v4
When linking VLCKit with libvlc v4, it will fail because of dav1d's assembly accelerated functions, whose symbols are not found in the static library despite linking it. This affects all platforms supported by VLCKit.
Typical symbols names affected are: _dav1d_prep_8tap_smooth_8bpc_neon _dav1d_inv_txfm_add_adst_flipadst_8x8_avx2 _dav1d_inv_txfm_add_adst_flipadst_8x8_ssse3