[libwebm] apply upstream changes to support Android NDK r15b and later

[jwtowner]

This applies a minimal set of upstream changes from the master branch of libwebm to 1.0.0.27 in order to support building with Android NDK r15b and later up through Android NDK r23 beta. This was primarily tested with Android NDK r21e and Android NDK r22.

Commits taken from https://chromium.googlesource.com/webm/libwebm master branch:

0ae757087f5e6eb01dfea16cc09205b2425cfb74
Fix android build failure with NDK r15b.

90967863b2f67962f52595a26abb8e4fa4105d44
mkvparser: fix float conversion warning

EDIT: This PR allows building libwebm for the android community triplets.

[NancyLi1013]

Could you please update

file(COPY ${SOURCE_PATH}/LICENSE.TXT DESTINATION ${CURRENT_PACKAGES_DIR}/share/libwebm)
file(RENAME ${CURRENT_PACKAGES_DIR}/share/libwebm/LICENSE.TXT ${CURRENT_PACKAGES_DIR}/share/libwebm/copyright)

as

file(INSTALL ${SOURCE_PATH}/LICENSE.TXT DESTINATION ${CURRENT_PACKAGES_DIR}/share/${PORT} RENAME copyright)?

[jwtowner]

@NancyLi1013

Done! I've switched the portfile over to use file(INSTALL ... RENAME ...) when installing the copyright file as you've suggested.

[Hoikas]

Considering it's been a little over five years since the last release and that these patches came directly from upstream master, maybe it would be better to change this port to a live-at-head policy. Meaning, use a date based version-string and use the current HEAD in the portfile.

[jwtowner]

Considering it's been a little over five years since the last release and that these patches came directly from upstream master, maybe it would be better to change this port to a live-at-head policy. Meaning, use a date based version-string and use the current HEAD in the portfile.

Yeah, I agree, and I would be pleased to do the work for that. However, I'd like to do it after getting this PR merged if that's okay, so we at least have libwebm 1.0.0.27 to fallback to for a time in case we run into other problems or dependency issues, and for those using port versioning. With this PR, I at least have it working on Windows, UWP, Android, Linux, iOS and macOS targets at the current version.

[ras0219-msft]

Awesome PR, thanks for the history/summary, it really helps!