Add a decoder only library for WebP in CMake.
Add a decoder only library for WebP in CMake.

Other libraries are also cleaned to automatically read the Makefile.am.
Dependencies also got cleaned.

Change-Id: I5d1ff0a4010d59e8c929ed0c9c30c05d83c271f8

PKRoma/libwebp,webmproject/libwebp,webmproject/libwebp,webmproject/libwebp,PKRoma/libwebp,PKRoma/libwebp,PKRoma/libwebp,webmproject/libwebp,webmproject/libwebp,PKRoma/libwebp,PKRoma/libwebp