[release-branch.go1.12] cmd/vendor/golang.org/x/tools/go/analysis: update from releas...

[release-branch.go1.12] cmd/vendor/golang.org/x/tools/go/analysis: update from release-branch.go1.12

$ ./update-xtools.sh
Copied /Users/rsc/src/golang.org/x/tools@aa829657 to .
$ cd ~/src/golang.org/x/tools
$ git log -n1 aa829657
commit aa82965741a9fecd12b026fbb3d3c6ed3231b8f8 (HEAD -> release-branch.go1.12, origin/release-branch.go1.12)
Author:     Daniel Martí <mvdan@mvdan.cc>
AuthorDate: Fri Mar 1 11:00:19 2019 +0000
Commit:     Brad Fitzpatrick <bradfitz@golang.org>
CommitDate: Wed Mar 13 21:06:03 2019 +0000
...
$

Picks up cmd/vet fixes that have been inadvertently missed in point releases so far.

Fixes #30399.
Fixes #30465.

Change-Id: Ibcfaac51d134205b986b32f857d54006b19c896a
Reviewed-on: https://go-review.googlesource.com/c/go/+/174519
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>