runtime: limit TestCgoCCodeSIGPROF test to 1 second

Still fails about 20% of the time on my laptop.

Fixes #14766.

Change-Id: I169ab728c6022dceeb91188f5ad466ed6413c062
Reviewed-on: https://go-review.googlesource.com/20590
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/testdata/testprogcgo/aprof.go

@@ -17,6 +17,7 @@ import (
 	"bytes"
 	"fmt"
 	"runtime/pprof"
+	"time"
 )
 
 func init() {
@@ -31,7 +32,13 @@ func CgoCCodeSIGPROF() {
 	go func() {
 		for {
 			<-c
+			start := time.Now()
 			for i := 0; i < 1e7; i++ {
+				if i%1000 == 0 {
+					if time.Since(start) > time.Second {
+						break
+					}
+				}
 				C.GoNop()
 			}
 			c <- true