[lld][WebAssembly] Cleanup output of --verbose

Remove some unnecessary logging from wasm-ld when running under
`--verbose`.  Unlike `-debug` this logging is available in release
builds.  This change makes it little more minimal/readable.

Also, avoid compiling the `debugWrite` function in releaase builds
where it does nothing.  This should remove a lot debug strings from
the binary, and avoid having to construct unused debug strings at
runtime.

Differential Revision: https://reviews.llvm.org/D109583