AFAICT https://github.com/carbon-language/carbon-lang/pull/4363 made
builds of extract.cpp go from ~15s to ~35s. I'm not sure how to really
improve on this, short of adding boilerplate to the types in order to
reduce template use (e.g., instead of using struct reflection to return
fields, we could have something that directly returns fields). But, this
switch to `MaybeTrace` seems to be about a 20% build time improvement
(down to ~30s), with `noinline` accounting for a part of that.
Jon Ross-Perkins
0ca0d0d4f5