runtime: ignore EAGAIN from exec in TestCgoExecSignalMask

Fixes #27731

Change-Id: Ifb4d57923b1bba0210ec1f623d779d7b5f442812
Reviewed-on: https://go-review.googlesource.com/135995
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/testdata/testprogcgo/exec.go

@@ -75,6 +75,14 @@ func CgoExecSignalMask() {
 					cmd.Stdout = os.Stdout
 					cmd.Stderr = os.Stderr
 					if err := cmd.Run(); err != nil {
+						// An overloaded system
+						// may fail with EAGAIN.
+						// This doesn't tell us
+						// anything useful; ignore it.
+						// Issue #27731.
+						if isEAGAIN(err) {
+							return
+						}
 						fmt.Printf("iteration %d: %v\n", j, err)
 						os.Exit(1)
 					}
@@ -87,3 +95,11 @@ func CgoExecSignalMask() {
 
 	fmt.Println("OK")
 }
+
+// isEAGAIN reports whether err is an EAGAIN error from a process execution.
+func isEAGAIN(err error) bool {
+	if p, ok := err.(*os.PathError); ok {
+		err = p.Err
+	}
+	return err == syscall.EAGAIN
+}