cmd/go: respect $GOBIN always
Another attempt at https://golang.org/cl/
5754088.
Before, we only consulted $GOBIN for source code
found in $GOROOT, but that's confusing to explain
and less useful. The new behavior lets users set
GOBIN=$HOME/bin and have all go-compiled binaries
installed there.
Tested a few cases in test.bash.
Ran all.bash with and without $GOBIN and it works.
Even so, I expect it to break the builders,
like it did last time, we can debug from there.
Fixes #3269 (again).
Fixes #3396.
Fixes #3397.
R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/
5927051