Fix CMake with WASM.
Fix CMake with WASM.

Change-Id: I21c78999484815c58b5b2c9795310da9d04888e9

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