Add support to build libwebm_mkvparser am: 9b9d173255 am: e6290beaea

Original change: https://android-review.googlesource.com/c/platform/external/libwebm/+/2242951

Change-Id: I137af59e1491973f76174f987809cdadb23ccbf6
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>