go/internal/gccgoimporter: add missing copyright notice
go/internal/gccgoimporter: add missing copyright notice

Change-Id: I2a1d5132f7263d8dc0e2a42c42b37b9d962a3ab7
Reviewed-on: https://go-review.googlesource.com/c/142892
Reviewed-by: Alan Donovan <7069e9552f9d110b0a0f326b96f22f63fb99dfc1@google.com>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools