runtime: For c-archive/c-shared, install signal handlers synchronously.

This is a port of https://golang.org/cl/18150 to the gccgo runtime.
    
    The previous behaviour of installing the signal handlers in a separate
    thread meant that Go initialization raced with non-Go initialization if
    the non-Go initialization also wanted to install signal handlers.  Make
    installing signal handlers synchronous so that the process-wide behavior
    is predictable.
    
    Reviewed-on: https://go-review.googlesource.com/19494

From-SVN: r233393

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-28a9dfbc3cda0bf7fd4f3fb1506c547f6cdf41a5
+22278c6e8ce3982b09111183bc6addf0184bef1f
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/runtime/go-libmain.c

@@ -59,6 +59,10 @@ initfn (int argc, char **argv, char** env __attribute__ ((unused)))
   struct args *a;
   pthread_t tid;
 
+  runtime_isarchive = true;
+
+  runtime_initsig(true);
+
   a = (struct args *) malloc (sizeof *a);
   if (a == NULL)
     die ("malloc", errno);
@@ -88,8 +92,6 @@ gostart (void *arg)
 {
   struct args *a = (struct args *) arg;
 
-  runtime_isarchive = true;
-
   if (runtime_isstarted)
     return NULL;
   runtime_isstarted = true;

libgo/runtime/proc.c

@@ -1093,7 +1093,7 @@ runtime_mstart(void* mp)
 			runtime_newextram();
 			runtime_needextram = 0;
 		}
-		runtime_initsig();
+		runtime_initsig(false);
 	}
 	
 	if(m->mstartfn)

libgo/runtime/runtime.h

@@ -550,7 +550,7 @@ void*	runtime_mal(uintptr);
 String	runtime_gostring(const byte*);
 String	runtime_gostringnocopy(const byte*);
 void	runtime_schedinit(void);
-void	runtime_initsig(void);
+void	runtime_initsig(bool);
 void	runtime_sigenable(uint32 sig);
 void	runtime_sigdisable(uint32 sig);
 void	runtime_sigignore(uint32 sig);

libgo/runtime/signal_unix.c

@@ -13,11 +13,16 @@
 extern SigTab runtime_sigtab[];
 
 void
-runtime_initsig(void)
+runtime_initsig(bool preinit)
 {
 	int32 i;
 	SigTab *t;
 
+	// For c-archive/c-shared this is called by go-libmain.c with
+	// preinit == true.
+	if(runtime_isarchive && !preinit)
+		return;
+
 	// First call: basic setup.
 	for(i = 0; runtime_sigtab[i].sig != -1; i++) {
 		t = &runtime_sigtab[i];
@@ -37,6 +42,9 @@ runtime_initsig(void)
 			}
 		}
 
+		if(runtime_isarchive && (t->flags&SigPanic) == 0)
+			continue;
+
 		t->flags |= SigHandling;
 		runtime_setsig(i, runtime_sighandler, true);
 	}