dashboard: skip riscv64 with a TODO in TestTryBotsCompileAllPorts

A trybot for linux/riscv64 still needs to be added. That work is
being tracked in issue golang.org/issue/36871.

Fix the failing test by skipping riscv64 for now, because a failing
test makes it hard to make other unrelated changes in x/build.

Updates golang/go#36871
Updates golang/go#27532

Change-Id: Ibbd17cd068c8eedc409ee5677074a404e6ac6d65
Reviewed-on: https://go-review.googlesource.com/c/build/+/216841
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

dashboard/builders_test.go

diff --git a/dashboard/builders_test.go b/dashboard/builders_test.go
index 2bee242..4ae7202 100644
--- a/dashboard/builders_test.go
+++ b/dashboard/builders_test.go
@@ -780,6 +780,9 @@
 			// up enough for e.g. compiling android-386
 			// from linux-amd64. (Issue #35596 too)
 			return
+		} else if goarch == "riscv64" {
+			// TODO(golang.org/issue/36871): Add a misc-compile trybot (or a real trybot).
+			return
 		}
 		goosArch := goos + "-" + goarch
 		if done[goosArch] {