cmd/dist: skip spectralnorm shootout test on the linux-arm-arm5 builder

Temporary fix to get the arm5 builder happy again.

Without hardware floating point, this test takes over 20 minutes to
run.

A proper solution would probably be to run all the benchmark tests,
but with a much lower iteration count, just to exercise the code.

Updates golang/go#12688

Change-Id: Ie56c93d3bf2a5a693a33217ba1b1df3c6c856442
Reviewed-on: https://go-review.googlesource.com/14775Reviewed-by: Dave Cheney <dave@cheney.net>
Reviewed-by: Minux Ma <minux@golang.org>

src/cmd/dist/test.go

@@ -451,6 +451,11 @@ func (t *tester) registerTests() {
 		t.registerTest("wiki", "../doc/articles/wiki", "./test.bash")
 		t.registerTest("codewalk", "../doc/codewalk", "time", "./run")
 		for _, name := range t.shootoutTests() {
+			if name == "spectralnorm" && os.Getenv("GO_BUILDER_NAME") == "linux-arm-arm5" {
+				// Heavy on floating point and takes over 20 minutes with softfloat.
+				// Disabled per Issue 12688.
+				continue
+			}
 			t.registerTest("shootout:"+name, "../test/bench/shootout", "time", "./timing.sh", "-test", name)
 		}
 	}