cmd/vet/all applies vet to all packages in the standard tree.
It is run for every configuration using this command:
  GO_BUILDER_NAME=misc-vetall go tool dist test
by the misc-vetall builder (see chart at build.golang.org).

Ideally we would switch to 'go vet', but it effectively does a partial
build. This means that its analysis has accurate type information, so
it reports slightly fewer spurious diagnostics. However, it is more
than twice as slow.

Instead, cmd/vet/all builds and runs
golang.org/x/tools/go/analysis/cmd/vet, which uses x/tools/go/packages
to load the entire std lib from source. It takes about 4min to run all
OS/ARCH pairs. An important consequence is that golang.org/x/tools
must be on your $GOPATH to run cmd/vet/all. The test has been
temporarily modified to warn and skip if this is not the case.

This is a preparatory step for switching to the new
cmd/vet based on vet-lite.

Whitelist changes:
- The two "deadcode" diagnostics removed from the whitelist were due
  to if-conditions that could now be proven false.
- The asmdecl warnings are now printed with the log.Printf prefix,
  so they are discarded by the parser and needn't be whitelisted.

Change-Id: I6486508b0de2cd947c897523af086a408cbaf4a8
Reviewed-on: https://go-review.googlesource.com/c/149097Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>