Usually, when we increment counters for flags, the counter only contains
the flag name. For the buildmode flag, we now include the flag value
because there's a limited set of values.
We can't use CountFlags directly anymore since we have different
behavior for buildmode.
Change-Id: I956a1a97d62850df3199b5514ad507ea51355c9f
Reviewed-on: https://go-review.googlesource.com/c/go/+/582896
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Sam Thanawalla <samthanawalla@google.com>