Sync-patch with libwebp ver 0.4.1-rc1.

Sync-patch with libwebp ver 0.4.1-rc1 (change#I5346984d2).
  - NEON assembly optimizations:
    - ~25% faster lossy decode / encode (-m 4)
    - ~10% faster lossless decode
    - ~5-10% faster lossless encode (-m 3/4)
  - Arch64 (arm64) & MIPS support/optimizations.

Change-Id: I855b65cec8fad5ec567c276b698e7714dc4bffd2
93 files changed