cmd/{cover,go}: revise fix for pkg init order change with -cover
This patch contains a revised fix for issue #56293, switching to a
scheme in which coverage counter variables and meta-data variables are
written to a separate output file as opposed to being tacked onto the
end of an existing rewritten source file.
The advantage of writing counter vars to a separate file is that the
Go command can then present that file as the first source file to the
compiler when the package is built; this will ensure that counter
variable are treated as lexically "before" any other variable that
might call an instrumented function as part of its initializer.
Updates #56293.
Change-Id: Iccb8a6532b976d36ccbd5a2a339882d1f5d19477
Reviewed-on: https://go-review.googlesource.com/c/go/+/499215 Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Bryan Mills <bcmills@google.com>