cmd/go: look for tool build ID before hashing entire file

Also fix the key used to store the ID.

This is a significant speedup in cmd/go run time.

Change-Id: Ie4c2f945872204fe24118d2adb2163f498d4394e
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/194257
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
1 file changed