lint: add "make lint" target, run it from ci

See https://github.com/tinygo-org/tinygo/issues/4225

Runs in both circleci and github, circleci is run on branch push, github is run on PR

Revive builds so fast, don't bother installing it; saves us wondering which one we get

Uses tools.go idiom to give control over linter versions to go.mod.

Also pacifies linter re AppendToGlobal as a token first fix.

TODO: gradually expand the number of directories that are linted,
uncomment more entries in revive.toml, and fix or suppress the
warnings lint finds.

TODO: add linters "go vet" and staticcheck

NOT TODO: don't add metalinters like golangci-lint that pull in
lots of new of dependencies; we'd rather not clutter go.mod that
much, let alone open ourselves up to the additional attack surface.

.circleci/config.yml

@@ -88,7 +88,7 @@ commands:
               # Do this before gen-device so that it doesn't check the
               # formatting of generated files.
               name: Check Go code formatting
-              command: make fmt-check
+              command: make fmt-check lint
       - run: make gen-device -j4
       - run: make smoketest XTENSA=0
       - save_cache: