The tests for go/types depend on reading gc export data from the
$GOROOT/pkg directory. This is the first use of these files as
testdata, so previously they were not copied to the android device.
Now they are used, copy them.

Fixes android/arm build.

Change-Id: If13bbe603ce0aff697a73a97ae9a7d6b3ea800f9
Reviewed-on: https://go-review.googlesource.com/8624Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>