Firefox broken on aarch64 due to libwebrtc

[Tobias Nygren <tnn%NetBSD.org@localhost>]

Hi!

Firefox fails with:
ld: ../../../third_party/libwebrtc/common_audio/common_audio_c_gn/Unified_c_common_audio_c_gn1.o:(.data.rel.ro.local.WebRtcSpl_CrossCorrelation+0x0): undefined reference to `WebRtcSpl_CrossCorrelationNeon'
... and more similar errors.

It looks like cross_correlation_neon.c does not get built but
is expected to be. The libwebrtc build system is weird to say the least
and there's a 700kB undocumented patch blob in patch-libwebrtc.diff.
I'm not sure how to fix this. Might have something to do with the
WEBRTC_HAS_NEON define. Any ideas? Thanks.

Kind regards,
-Tobias