Fix debug symbols logic on platform=web to match Godot core.

[BenLubar]

Currently, building with platform=web debug_symbols=yes does not produce debug symbols.

[dsnopek]

Thanks!

I haven't tested, but this matches what we have in Godot, so I think it should be good

[dsnopek]

@enetheru What do we need to do (if anything) to do this for CMake as well?

[enetheru]

@enetheru What do we need to do (if anything) to do this for CMake as well?

@dsnopek
Nothing, CMake has its own mechanism for choosing to add the correct flags for debug symbols.
Either the variable CMAKE_BUILD_TYPE of either Debug or RelWithDebInfo for single configuration builders.
Or the --config option with the same values as above for multi-configuration builders.

[dsnopek]

@enetheru Awesome, thanks!