runtime: use startpanic so that only one thread handles an incoming SIGQUIT

Typing ^\ delivers the SIGQUIT to all threads, it appears.

R=golang-dev, r, iant
CC=golang-dev
https://golang.org/cl/5657044

src/pkg/runtime/signal_darwin_386.c

@@ -92,9 +92,7 @@ runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp)
 		return;
 
 Throw:
-	if(runtime·panicking)	// traceback already printed
-		runtime·exit(2);
-	runtime·panicking = 1;
+	runtime·startpanic();
 
 	if(sig < 0 || sig >= NSIG){
 		runtime·printf("Signal %d\n", sig);

src/pkg/runtime/signal_darwin_amd64.c

@@ -102,9 +102,7 @@ runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp)
 		return;
 
 Throw:
-	if(runtime·panicking)	// traceback already printed
-		runtime·exit(2);
-	runtime·panicking = 1;
+	runtime·startpanic();
 
 	if(sig < 0 || sig >= NSIG){
 		runtime·printf("Signal %d\n", sig);

src/pkg/runtime/signal_freebsd_386.c

@@ -89,9 +89,7 @@ runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp)
 		return;
 
 Throw:
-	if(runtime·panicking)	// traceback already printed
-		runtime·exit(2);
-	runtime·panicking = 1;
+	runtime·startpanic();
 
 	if(sig < 0 || sig >= NSIG)
 		runtime·printf("Signal %d\n", sig);

src/pkg/runtime/signal_freebsd_amd64.c

@@ -97,9 +97,7 @@ runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp)
 		return;
 
 Throw:
-	if(runtime·panicking)	// traceback already printed
-		runtime·exit(2);
-	runtime·panicking = 1;
+	runtime·startpanic();
 
 	if(sig < 0 || sig >= NSIG)
 		runtime·printf("Signal %d\n", sig);

src/pkg/runtime/signal_linux_386.c

@@ -85,9 +85,7 @@ runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp)
 		return;
 
 Throw:
-	if(runtime·panicking)	// traceback already printed
-		runtime·exit(2);
-	runtime·panicking = 1;
+	runtime·startpanic();
 
 	if(sig < 0 || sig >= NSIG)
 		runtime·printf("Signal %d\n", sig);

src/pkg/runtime/signal_linux_amd64.c

@@ -95,9 +95,7 @@ runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp)
 		return;
 
 Throw:
-	if(runtime·panicking)	// traceback already printed
-		runtime·exit(2);
-	runtime·panicking = 1;
+	runtime·startpanic();
 
 	if(sig < 0 || sig >= NSIG)
 		runtime·printf("Signal %d\n", sig);

src/pkg/runtime/signal_netbsd_386.c

@@ -85,9 +85,7 @@ runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp)
 		return;
 
 Throw:
-	if(runtime·panicking)	// traceback already printed
-		runtime·exit(2);
-	runtime·panicking = 1;
+	runtime·startpanic();
 
 	if(sig < 0 || sig >= NSIG)
 		runtime·printf("Signal %d\n", sig);

src/pkg/runtime/signal_netbsd_amd64.c

@@ -94,9 +94,7 @@ runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp)
 		return;
 
 Throw:
-	if(runtime·panicking)	// traceback already printed
-		runtime·exit(2);
-	runtime·panicking = 1;
+	runtime·startpanic();
 
 	if(sig < 0 || sig >= NSIG)
 		runtime·printf("Signal %d\n", sig);

src/pkg/runtime/signal_openbsd_386.c

@@ -85,9 +85,7 @@ runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp)
 		return;
 
 Throw:
-	if(runtime·panicking)	// traceback already printed
-		runtime·exit(2);
-	runtime·panicking = 1;
+	runtime·startpanic();
 
 	if(sig < 0 || sig >= NSIG)
 		runtime·printf("Signal %d\n", sig);

src/pkg/runtime/signal_openbsd_amd64.c

@@ -94,9 +94,7 @@ runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp)
 		return;
 
 Throw:
-	if(runtime·panicking)	// traceback already printed
-		runtime·exit(2);
-	runtime·panicking = 1;
+	runtime·startpanic();
 
 	if(sig < 0 || sig >= NSIG)
 		runtime·printf("Signal %d\n", sig);