cmd/compile: substitute "". prefix with package in more import locations
cmd/compile: substitute "". prefix with package in more import locations

The "" stand-in for the current package needs to be substituted
in more places when importing, because of generics.

""..dict.conv4["".MyString]

when imported in main and then exported, this becomes

a..dict.conv4["".MyString]

and then the linker makes that into

a..dict.conv4[main.MyString]

Which isn't correct. We need to replace on import not just
function names, but also globals, which this CL does.

Change-Id: Ia04a23b5ffd60aeeaba72c807f69261105670f8e
Reviewed-on: https://go-review.googlesource.com/c/go/+/356570
Trust: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>
Trust: Dan Scales <7338a4f274e3bf1354488b9d1f344f4c9a69a8fb@google.com>
Run-TryBot: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Dan Scales <7338a4f274e3bf1354488b9d1f344f4c9a69a8fb@google.com>

golang/go,golang/go,golang/go,CAFxX/go,nawawi/go,cloudflare/go,cloudflare/go,cloudflare/go,nawawi/go,CAFxX/go,golang/go,cloudflare/go,nawawi/go,cloudflare/go,nawawi/go,golang/go,cloudflare/go,CAFxX/go,nawawi/go,golang/go,CAFxX/go,nawawi/go,nawawi/go,cloudflare/go,CAFxX/go,cloudflare/go,CAFxX/go,CAFxX/go,CAFxX/go,golang/go,nawawi/go,golang/go