runtime, testing: support Goexit, SkipNow, FailNow

Keep a pending Goexit separate from the active panic state so recovered
deferred panics do not cancel the original Goexit unwind. Goexit should
also ignore -panic=trap, since it is not a panic.

Wire testing.FailNow and SkipNow through runtime.Goexit, and run tests
and benchmarks in goroutines. This lets Goexit terminate the user
function without skipping test bookkeeping. Add Goexit/recover coverage
and enable crypto/ecdh in the Linux stdlib test list.

src/testing/benchmark.go

@@ -179,7 +179,12 @@ func (b *B) run1() bool {
 			ctx.maxLen = n + 8 // Add additional slack to avoid too many jumps in size.
 		}
 	}
-	b.runN(1)
+	done := make(chan struct{})
+	go func() {
+		defer close(done)
+		b.runN(1)
+	}()
+	<-done
 	return !b.hasSub
 }
 
@@ -195,8 +200,12 @@ func (b *B) run() {
 }
 
 func (b *B) doBench() BenchmarkResult {
-	// in upstream, this uses a goroutine
-	b.launch()
+	done := make(chan struct{})
+	go func() {
+		defer close(done)
+		b.launch()
+	}()
+	<-done
 	return b.result
 }
 

src/testing/testing.go

@@ -214,9 +214,8 @@ func (c *common) Failed() bool {
 // current goroutine).
 func (c *common) FailNow() {
 	c.Fail()
-
 	c.finished = true
-	c.Error("FailNow is incomplete, requires runtime.Goexit()")
+	runtime.Goexit()
 }
 
 // log generates the output.
@@ -288,7 +287,7 @@ func (c *common) Skipf(format string, args ...any) {
 func (c *common) SkipNow() {
 	c.skip()
 	c.finished = true
-	c.Error("SkipNow is incomplete, requires runtime.Goexit()")
+	runtime.Goexit()
 }
 
 func (c *common) skip() {
@@ -480,19 +479,19 @@ type InternalTest struct {
 }
 
 func tRunner(t *T, fn func(t *T)) {
+	t.start = time.Now()
 	defer func() {
+		t.duration += time.Since(t.start) // TODO: capture cleanup time, too.
 		t.runCleanup()
+		t.report() // Report after all subtests have finished.
+		if t.parent != nil && !t.hasSub {
+			t.setRan()
+		}
 	}()
 
 	// Run the test.
-	t.start = time.Now()
 	fn(t)
-	t.duration += time.Since(t.start) // TODO: capture cleanup time, too.
-
-	t.report() // Report after all subtests have finished.
-	if t.parent != nil && !t.hasSub {
-		t.setRan()
-	}
+	t.finished = true
 }
 
 // Run runs f as a subtest of t called name. It waits until the subtest is finished
@@ -524,7 +523,12 @@ func (t *T) Run(name string, f func(t *T)) bool {
 		fmt.Fprintf(t.output, "=== RUN   %s\n", sub.name)
 	}
 
-	tRunner(&sub, f)
+	done := make(chan struct{})
+	go func() {
+		defer close(done)
+		tRunner(&sub, f)
+	}()
+	<-done
 	return !sub.failed
 }