cmd/gc: fix race detector on tail-call wrappers

(By not using the tail-call wrappers when the race
detector is enabled.)

R=golang-dev, minux.ma, dvyukov, daniel.morsing
CC=golang-dev
https://golang.org/cl/10227043

src/cmd/gc/go.h

@@ -268,7 +268,6 @@ struct	Node
 	uchar	dupok;	// duplicate definitions ok (for func)
 	schar	likely; // likeliness of if statement
 	uchar	hasbreak;	// has break statement
-	uchar	norace;	// disable race detector for this function
 	uint	esc;		// EscXXX
 	int	funcdepth;
 

src/cmd/gc/racewalk.c

@@ -58,7 +58,7 @@ racewalk(Node *fn)
 	Node *nodpc;
 	char s[1024];
 
-	if(fn->norace || ispkgin(omit_pkgs, nelem(omit_pkgs)))
+	if(ispkgin(omit_pkgs, nelem(omit_pkgs)))
 		return;
 
 	if(!ispkgin(noinst_pkgs, nelem(noinst_pkgs))) {

src/cmd/gc/subr.c

@@ -2573,11 +2573,9 @@ genwrapper(Type *rcvr, Type *method, Sym *newnam, int iface)
 	dot = adddot(nod(OXDOT, this->left, newname(method->sym)));
 	
 	// generate call
-	if(isptr[rcvr->etype] && isptr[methodrcvr->etype] && method->embedded && !isifacemethod(method->type)) {
+	if(!flag_race && isptr[rcvr->etype] && isptr[methodrcvr->etype] && method->embedded && !isifacemethod(method->type)) {
 		// generate tail call: adjust pointer receiver and jump to embedded method.
-		fn->norace = 1; // something about this body makes the race detector unhappy.
-		// skip final .M
-		dot = dot->left;
+		dot = dot->left;	// skip final .M
 		if(!isptr[dotlist[0].field->type->etype])
 			dot = nod(OADDR, dot, N);
 		as = nod(OAS, this->left, nod(OCONVNOP, dot, N));