runtime: print goroutine header on fault

I've just needed the G status on fault to debug runtime bug.
For some reason we print everything except header here.
Make it more informative and consistent.

R=rsc
CC=golang-codereviews
https://golang.org/cl/67870056

src/pkg/runtime/signal_386.c

@@ -112,6 +112,7 @@ Throw:
 	runtime·printf("\n");
 
 	if(runtime·gotraceback(&crash)){
+		runtime·goroutineheader(gp);
 		runtime·traceback(SIG_EIP(info, ctxt), SIG_ESP(info, ctxt), 0, gp);
 		runtime·tracebackothers(gp);
 		runtime·printf("\n");

src/pkg/runtime/signal_amd64.c

@@ -122,6 +122,7 @@ Throw:
 	runtime·printf("\n");
 
 	if(runtime·gotraceback(&crash)){
+		runtime·goroutineheader(gp);
 		runtime·traceback(SIG_RIP(info, ctxt), SIG_RSP(info, ctxt), 0, gp);
 		runtime·tracebackothers(gp);
 		runtime·printf("\n");

src/pkg/runtime/signal_arm.c

@@ -112,6 +112,7 @@ Throw:
 	runtime·printf("\n");
 
 	if(runtime·gotraceback(&crash)){
+		runtime·goroutineheader(gp);
 		runtime·traceback(SIG_PC(info, ctxt), SIG_SP(info, ctxt), SIG_LR(info, ctxt), gp);
 		runtime·tracebackothers(gp);
 		runtime·printf("\n");