cmd/api: run api check on all ports

[prattmic]

cmd/api runs only on a fixed set of ports. The list is strange, excluding some first-class ports (linux/arm64, darwin/arm64), but including several secondary ports. Any ports excluded from this list get no checking at all.

Inspired by a suggestion from @bcmills, I think we should adjust behavior:

• cmd/api should always include the current GOOS/GOARCH(/CGO_ENABLED).
• The default context set should include all first-class ports.
• cmd/dist should perhaps tell cmd/api to only check the current GOOS/GOARCH, to avoid duplicate work in builders.

These changes should make all first-class and secondary ports covered by api checks, in each of their respective builders (pre-submit or post-submit depending on which ports are included in TryBots, as usual).

cc @golang/release

[prattmic]

• cmd/dist should perhaps tell cmd/api to only check the current GOOS/GOARCH, to avoid duplicate work in builders.

dist skips the API test on android, ios, js, and plan9 because they are too slow. Those could perhaps be covered in one of the misc-compile builders? Or maybe a single api builder just runs every port?

[bcmills]

We have a distinction between short and long tests. Maybe the short test (the default) should run the current GOOS/GOARCH, and the long test should also run every first-class GOOS/GOARCH?

(That would carve out the android, ios, js, and plan9 builders incidentally, because none of those are configured as -longtest.)

[bcmills]

compare #14892 / CL 322309 (CC @iwdgo)

[bcmills]

Those could perhaps be covered in one of the misc-compile builders? Or maybe a single api builder just runs every port?

Running them on the misc-compile builders sounds appropriate to me. IIRC the misc-compile builders also run go vet on their port, and the API check is conceptually very similar to a vet check.

[bcmills]

For reference, cmd/coordinator currently has a special case for the api test:
https://cs.opensource.google/go/x/build/+/master:dashboard/builders.go;l=1217-1226;drc=59e7a6bb02dba3fc4a32b23dc98b96d04453d1e1

Probably a good first step would be to move that logic into the api test itself (having it skip itself based on GO_BUILDER_NAME) and removing that special case from the coordinator so that we can iterate on it without redeploying the coordinator.