cgo: supports c/go callback funcs

ssa/decl.go

@@ -117,6 +117,10 @@ func (g Global) InitNil() {
 	g.impl.SetInitializer(llvm.ConstNull(g.impl.GlobalValueType()))
 }
 
+func (g Global) ReplaceAllUsesWith(v Expr) {
+	g.impl.ReplaceAllUsesWith(v.impl)
+}
+
 // -----------------------------------------------------------------------------
 
 // Function represents the parameters, results, and code of a function

ssa/expr.go

@@ -59,6 +59,15 @@ func (v Expr) SetOrdering(ordering AtomicOrdering) Expr {
 	return v
 }
 
+func (v Expr) SetName(alias string) Expr {
+	v.impl.SetName(alias)
+	return v
+}
+
+func (v Expr) Name() string {
+	return v.impl.Name()
+}
+
 // -----------------------------------------------------------------------------
 
 type builtinTy struct {