Add support to build libwebm_mkvparser am: 9b9d173255

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

Change-Id: I3351883f78cbdff442bd899ae33083598dd389c3
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>