misc/swig: move tests to cmd/cgo/internal
This moves the misc/swig test to cmd/cgo/internal.
This lets these tests access facilities in internal/testenv. It's also
now just a normal test that can run as part of the cmd tests.
For #37486.
Change-Id: Ibe5026219999d175aa0a310b9886bef3f6f9ed17
Reviewed-on: https://go-review.googlesource.com/c/go/+/492722
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>