Enable -Wextra in C++ builds (#1294)

Summary:
Pull Request resolved: https://github.com/facebook/yoga/pull/1294

X-link: https://github.com/facebook/react-native/pull/37383

Add -Wextra to the build, and fixup some more instances of -Wunused-parameter that it sufaces which were not automatically fixable.

Reviewed By: javache

Differential Revision: D45772846

fbshipit-source-id: 680498f66f2104c29a71366bf30dba8895d9baf4

cmake/project-defaults.cmake

@@ -33,6 +33,7 @@ add_compile_options(
     -fexceptions
     # Enable warnings and warnings as errors
     -Wall
+    -Wextra
     -Werror
     # Disable RTTI
     $<$<COMPILE_LANGUAGE:CXX>:-fno-rtti>