RelWithDebInfo debug names not working

[guybedford]

Unfortunately, building with RelWithDebInfo still doesn't seem to provide debugging information properly.

A simple test of this is to run a build with RelWithDebInfo and then print the starling-raw.wasm binary with wasm-tools print - function names are fully lost in the process.

Resolving this is a prerequisite to getting debugging going for ComponentizeJS in bytecodealliance/ComponentizeJS#137.

[guybedford]

This may be a bug in wasm-opt.