runtime: disable CPU profiling before removing the SIGPROF handler

Otherwise, in c-archive or c-shared mode, there is the chance of
getting a SIGPROF just after the signal handler is removed but before
profiling is disabled, in which case the program will die.

Fixes #46498

Change-Id: I5492beef45fec9fb9a7f58724356d6aedaf799ac
Reviewed-on: https://go-review.googlesource.com/c/go/+/329290
Trust: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

src/runtime/signal_unix.go

@@ -280,6 +280,8 @@ func setProcessCPUProfiler(hz int32) {
 		it.it_value = it.it_interval
 		setitimer(_ITIMER_PROF, &it, nil)
 	} else {
+		setitimer(_ITIMER_PROF, &itimerval{}, nil)
+
 		// If the Go signal handler should be disabled by default,
 		// switch back to the signal handler that was installed
 		// when we enabled profiling. We don't try to handle the case
@@ -303,8 +305,6 @@ func setProcessCPUProfiler(hz int32) {
 				setsig(_SIGPROF, h)
 			}
 		}
-
-		setitimer(_ITIMER_PROF, &itimerval{}, nil)
 	}
 }