Add a CMake option for WEBP_SWAP_16BIT_CSP.
Add a CMake option for WEBP_SWAP_16BIT_CSP.

Change-Id: I79ed6cbce9563bf7ca97fc2e10ec3e75b6b8ab5b

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