Tools:

cmd/dist: add list subcommand to list all supported platforms (CL 19837)
cmd/go: GO15VENDOREXPERIMENT gone, assumed on (CL 19615)
cmd/link: "-X name value" form gone (CL 19614)

Ports:

SOMETHING WILL HAPPEN

API additions and behavior changes:

runtime: add CallerFrames and Frames (CL 19869)