runtime/pprof: make TestBlockProfile more robust

It's using debug mode of pprof.writeBlock, so the output actually goes
through text/tabwriter. It is possible that tabwriter expands each tab
into multiple tabs in certain cases.

For example, this output has been observed on the new arm64 port:
10073805 1 @ 0x1088ec 0xd1b8c 0xd0628 0xb68c0 0x867f4
#	0x1088ec	sync.(*Cond).Wait+0xfc				/home/minux/go.git/src/sync/cond.go:63
#	0xd1b8c		runtime/pprof_test.blockCond+0x22c		/home/minux/go.git/src/runtime/pprof/pprof_test.go:454
#	0xd0628		runtime/pprof_test.TestBlockProfile+0x1b8	/home/minux/go.git/src/runtime/pprof/pprof_test.go:359
#	0xb68c0		testing.tRunner+0x140				/home/minux/go.git/src/testing/testing.go:447

10069965 1 @ 0x14008 0xd1390 0xd0628 0xb68c0 0x867f4
#	0x14008	runtime.chansend1+0x48				/home/minux/go.git/src/runtime/chan.go:76
#	0xd1390	runtime/pprof_test.blockChanSend+0x100		/home/minux/go.git/src/runtime/pprof/pprof_test.go:396
#	0xd0628	runtime/pprof_test.TestBlockProfile+0x1b8	/home/minux/go.git/src/runtime/pprof/pprof_test.go:359
#	0xb68c0	testing.tRunner+0x140				/home/minux/go.git/src/testing/testing.go:447

10069706 1 @ 0x108e0c 0xd193c 0xd0628 0xb68c0 0x867f4
#	0x108e0c	sync.(*Mutex).Lock+0x19c			/home/minux/go.git/src/sync/mutex.go:67
#	0xd193c		runtime/pprof_test.blockMutex+0xbc		/home/minux/go.git/src/runtime/pprof/pprof_test.go:441
#	0xd0628		runtime/pprof_test.TestBlockProfile+0x1b8	/home/minux/go.git/src/runtime/pprof/pprof_test.go:359
#	0xb68c0		testing.tRunner+0x140				/home/minux/go.git/src/testing/testing.go:447

Change-Id: I3bef778c5fe01a894cfdc526fdc5fecb873b8ade
Signed-off-by: Shenghou Ma <minux@golang.org>
Reviewed-on: https://go-review.googlesource.com/5554Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

src/runtime/pprof/pprof_test.go

@@ -375,7 +375,7 @@ func TestBlockProfile(t *testing.T) {
 	}
 
 	for _, test := range tests {
-		if !regexp.MustCompile(test.re).MatchString(prof) {
+		if !regexp.MustCompile(strings.Replace(test.re, "\t", "\t+", -1)).MatchString(prof) {
 			t.Fatalf("Bad %v entry, expect:\n%v\ngot:\n%v", test.name, test.re, prof)
 		}
 	}