add dec_wasm.c

stub + basic cmake support for targeting native code generation using
portable intrinsics / wasm (WebAssembly). integrating this into the
webp_js path will be left until the implementation is more complete.

Change-Id: I3e751b511f6d671da5ba8afc88ca412f31f097b0

cmake/cpu.cmake

@@ -116,3 +116,13 @@ foreach(I_SIMD RANGE ${WEBP_SIMD_FLAGS_RANGE})
     endif()
   endif()
 endforeach()
+
+## Add *_wasm.c files if enabled.
+if(WEBP_ENABLE_WASM)
+  file(GLOB SIMD_FILES "${CMAKE_CURRENT_LIST_DIR}/../"
+    "src/dsp/*_wasm.c"
+  )
+  foreach(FILE ${SIMD_FILES})
+    list(APPEND WEBP_SIMD_FILES_TO_INCLUDE ${FILE})
+  endforeach()
+endif()