This is needed since we're using AC_LANG_CPLUSPLUS

Makes syntax highlighting in vim unbreak.

On x86, SSE optimisations are always compiled in, and used based on
runtime checks.

On ARM, we try to autodetect NEON support (with an option of runtime
detection). This has not been build-tested on ARM yet.

This leaves MIPS to be done.

This isn't used it, but let's keep it up to date

Corresponds to upstream commit 524e9b043e7e86fd72353b987c9d5f6a1ebf83e1

Update notes:

 * Pull in third party license file

 * Replace .gypi files with BUILD.gn to keep track of what changes
   upstream

 * Bunch of new filse pulled in as dependencies

 * Won't build yet due to changes needed on top of these

Corresponds to upstream commit 524e9b043e7e86fd72353b987c9d5f6a1ebf83e1

Corresponds to upstream commit 524e9b043e7e86fd72353b987c9d5f6a1ebf83e1

Update notes:

 * Moved src/ to webrtc/ to easily diff against the third_party/webrtc
   in the chromium tree

 * ARM/NEON/MIPS support is not yet hooked up

 * Tests have not been copied

Very minor changes.

Just reorganisation of the audio_processing code.

Removes matlab tests, adds delay estimation logging, and some other
minor fixes/improvements.

Avoide the need to pull in protobuf and other related bits.