Make browser exports optional

[sbc100]

No description provided.

[kripken]

Do we automatically add helpful messages in debug builds for these? I am guessing maybe no, since I'm not sure we have a list that includes these particular functions atm. We have that for other things where the error message tells the user exactly what to do, which could be good here as well.

[sbc100]

Yes, we do. In debug builds if you try to call Module['anyLibraryFuncAtAll'] you will see this one of these two errors:

emscripten/src/runtime_debug.js

Line 65 in 04a0cad

var msg = `\`${sym}\` is a library symbol and not included by default; add it to your library.js __deps or to DEFAULT_LIBRARY_FUNCS_TO_INCLUDE on the command line`;

emscripten/src/runtime_debug.js

Line 92 in 04a0cad

var msg = `'${sym}' was not exported. add it to EXPORTED_RUNTIME_METHODS (see the Emscripten FAQ)`;

I locally verified this was the case with these changes, but we do have tests for that too.

[kripken]

Sounds good.

None of the code size tests measure this? Maybe we don't use browser code there.

[sbc100]

Sounds good.

None of the code size tests measure this? Maybe we don't use browser code there.

Yeah we don't have any code size measurement for things like Browser and FS (our most heavy weight APIs).