runtime: add runtime· prefix to showframe

R=ken2
CC=golang-dev
https://golang.org/cl/4978042

src/pkg/runtime/amd64/traceback.c

@@ -123,7 +123,7 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *g, int32 skip, uintptr
 		else if(pcbuf != nil)
 			pcbuf[n++] = pc;
 		else {
-			if(showframe(f)) {
+			if(runtime·showframe(f)) {
 				// Print during crash.
 				//	main(0x1, 0x2, 0x3)
 				//		/home/rsc/go/src/runtime/x.go:23 +0xf

src/pkg/runtime/arm/traceback.c

@@ -117,7 +117,7 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *g, int32 skip, uintptr
 		else if(pcbuf != nil)
 			pcbuf[n++] = pc;
 		else {
-			if(showframe(f)) {
+			if(runtime·showframe(f)) {
 				// Print during crash.
 				//	main(0x1, 0x2, 0x3)
 				//		/home/rsc/go/src/runtime/x.go:23 +0xf

src/pkg/runtime/symtab.c

@@ -496,7 +496,7 @@ contains(String s, int8 *p)
 }
 
 bool
-showframe(Func *f)
+runtime·showframe(Func *f)
 {
 	// return 1;  // for debugging - show all frames
 	return contains(f->name, ".") && !hasprefix(f->name, "runtime.");