Fix a few recently introduced code smells

[oleg-derevenetz]

• Don't create an empty anonymous namespace for non-Emscripten builds (code smell from SonarCloud);
• Limit the scope of the disabled Emscripten-specific -Wvariadic-macro-arguments-omitted warning.

[ihhub]

@oleg-derevenetz , thank you so much for this cleanup!