runtime: pass LR to sigprof on windows/arm

TestCPUProfileLabel was failing on windows/arm because the link register
was not being passed to sigprof(). The link register is required to
generate a correct traceback. With this change, all tests in runtime.pprof
are now passing.

Updates #26148

Change-Id: Ia693b34278dc08a98023751ff1a922d9eee8fdd6
Reviewed-on: https://go-review.googlesource.com/c/153839
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/os_windows.go

@@ -879,7 +879,7 @@ func profilem(mp *m, thread uintptr) {
 		gp = *((**g)(unsafe.Pointer(tls)))
 	}
 
-	sigprof(r.ip(), r.sp(), 0, gp, mp)
+	sigprof(r.ip(), r.sp(), r.lr(), gp, mp)
 }
 
 func profileloop1(param uintptr) uint32 {