Port from old compiler code to emit compilation flags into the source map

The 1.0 (or 1.1) compiler emitted the compilation flags into the source map. We added this for hypothetical tooling scenarios, where browser tools could trigger a simple recompilation of a file discovered by a source map, in the case where it was live edited.

This is not a high priority as those scenarios aren't currently planned, but perhaps it would be a simple port of work already done.