Sync-patch with libwebp ver 0.4.1, fix broken Google Play images on GCC 4.9+

This is the squashed commit of:
- Bringing libwebp to v0.4.1 (up to commit 80b8099fd8391d55c2a4ff7c1165c8ab786ed334 -> https://gerrit.chromium.org/gerrit/gitweb?p=webm/libwebp.git;a=commit;h=80b8099fd8391d55c2a4ff7c1165c8ab786ed334)
- Porting Android.mk for both decoder and encoder to 0.4.1 based on applied changes (added/removed things) and a bit of brain
- Moving include/webp to src/webp (same as libwebp), with leaving compatibility symbolic link in old directory (shouldn't be needed, but Google had to have reason for doing things like this. In fact, this is how it should be done in the first place)
- Fixing v0.4.1 derps, such as proper path for cpu-features.h header

Original author: Łukasz "JustArchi" Domeradzki <JustArchi@JustArchi.net>
Thanks to: 95A31 @ xda-developers.com for telling me the root of this issue

This commit fixes GCC 4.8.3+ 4.9+ PlayStore bug
References: https://bugs.launchpad.net/linaro/+bug/1332989 https://code.google.com/p/android/issues/detail?id=74557