It turns out that having "-g" in the compile-statement causes
Emscripten to pick -g3, which makes for very big binaries. This
is very likely not your intention when building Emscripten, as
smaller really is better.
For comparison, with RelWithDebInfo the binary is ~80MB. With
Release it is ~7.4MB.
When a developer attaches the "preview" label, a build is created
and published on https://preview.openttd.org/. After that, new
pushes to the PR are automatically build (as long as the "preview"
label exists).
If a non-developer attaches the "preview" label, it will be
removed.
Patric Stout