cmd/dist: add maymorestack tests
These tests run the runtime, reflect, and sync package tests with the
two maymorestack hooks we have.
These tests only run on the longtest builders (or with
GO_TEST_SHORT=false) because we're running the runtime test two
additional times and the mayMoreStackMove hook makes it about twice as
slow (~230 seconds).
To run just these tests by hand, do
GO_TEST_SHORT=false go tool dist test -run mayMoreStack
Updates #48297.
This detected #49354, which was found as a flake on the dashboard, but
was reliably reproducible with these tests; and #49395.
Change-Id: If785a8b8d6e1b9ad4d2ae67493b54055ab6cbc85
Reviewed-on: https://go-review.googlesource.com/c/go/+/361212
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Austin Clements <austin@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>