[wasm][build] Exclude Tools from build when BUILD_TOOLS is OFF

This is a follow up to 5e7281b, which
just adds the `BUILD_TOOLS` option but doesn't actually use it.

Author: kateinoigakukun

Sources/CMakeLists.txt

@@ -2,4 +2,6 @@ add_subdirectory(UUID)
 add_subdirectory(Foundation)
 add_subdirectory(FoundationNetworking)
 add_subdirectory(FoundationXML)
-add_subdirectory(Tools)
+if(BUILD_TOOLS)
+  add_subdirectory(Tools)
+endif()