libvpx: Update to version 1.7.0

[akien-mga]

cc @zaps166 as I have no clue how to do it. I had a look at the upstream tarball but it's not trivial to match it with our files.

When you get to it, please document the steps in thirdparty/README.md so that we know how to handle the update next time.

[zaps166]

Some files are generated manually (based on files generated during libvpx compilation), it is a rtcd directory.

ARM assembly files are converted using perl script as in libvpx compilation (armasm_ms, gas and gas_apple).

I've used only necessary files, so any other files are not exists in repository, so replace only existing files, remove non-existing files in newer version and add missing new files. Modify rtcd if necessary (this can be the most difficult, but maybe nothing changed in minor libvpx release :) )

Some files are modified, but not much (please look at commit from my PR - most of it is rtcd, so not many changes).

[akien-mga]

Kicking to 3.1, I won't have time to handle this myself as it seems far from trivial.

[ShyRed]

Is it possible to automate all the required steps with SCons so we just have to update the libvpx files and SCons does all the remaining tasks?

"converted using perl script" sounds like we could write some python script that is run by SCons instead. Same with "files are generated manually".

[guelinator]

i really would need this feature. now its postponed to 3.2...

[ShyRed]

libvpx recently released v1.8.0

Updating libvpx might fix #21568

[zaps166]

Updating a source code for new libvpx shoulnd't be a long task, but adding new library into a custom build system (+ necessary ASM files which are mandatory for decoding speed) took much longer time and it was much more difficult for me than writing a functionality in C++. I don't have time now for doing this now :(

When adding libvpx here I modified some source files and I've did some configuration based on what libvpx compilation scripts did. See comment #8334 (comment)

Maybe compiling libvpx library separately as a static lib and then linking it wouldn't be a bad idea? For people which wouldn't compile it manually there can be precompiled libraries somewhere.