runtime/coverage: add support for "auxiliary" meta-data files
Enhance the functions called by _testmain.go during "go test -cover"
test binary runs to allow for injection of extra or "auxiliary"
meta-data files when reporting coverage statistics. There are unit
tests for this functionality, but it is not yet wired up to be used by
the Go command yet, that will appear in a subsequent patch.
Change-Id: I10b79ca003fd7a875727dc1a86f23f58d6bf630c
Reviewed-on: https://go-review.googlesource.com/c/go/+/495451
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: David Chase <drchase@google.com>