runtime: move Itab to runtime.h

The 'type' field of Itab will be used by the garbage collector.

R=rsc
CC=golang-dev
https://golang.org/cl/6815059

src/pkg/runtime/iface.c

@@ -20,19 +20,6 @@ runtime·printeface(Eface e)
 	runtime·printf("(%p,%p)", e.type, e.data);
 }
 
-/*
- * layout of Itab known to compilers
- */
-struct Itab
-{
-	InterfaceType*	inter;
-	Type*	type;
-	Itab*	link;
-	int32	bad;
-	int32	unused;
-	void	(*fun[])(void);
-};
-
 static	Itab*	hash[1009];
 static	Lock	ifacelock;
 

src/pkg/runtime/runtime.h

@@ -62,6 +62,7 @@ typedef	struct	MCache		MCache;
 typedef	struct	FixAlloc	FixAlloc;
 typedef	struct	Iface		Iface;
 typedef	struct	Itab		Itab;
+typedef	struct	InterfaceType	InterfaceType;
 typedef	struct	Eface		Eface;
 typedef	struct	Type		Type;
 typedef	struct	ChanType		ChanType;
@@ -322,6 +323,17 @@ struct	Func
 	int32	locals;	// number of 32-bit locals
 };
 
+// layout of Itab known to compilers
+struct	Itab
+{
+	InterfaceType*	inter;
+	Type*	type;
+	Itab*	link;
+	int32	bad;
+	int32	unused;
+	void	(*fun[])(void);
+};
+
 struct	WinCall
 {
 	void	(*fn)(void*);
@@ -823,7 +835,7 @@ void	runtime·chansend(ChanType*, Hchan*, byte*, bool*, void*);
 void	runtime·chanrecv(ChanType*, Hchan*, byte*, bool*, bool*);
 bool	runtime·showframe(Func*);
 
-void	runtime·ifaceE2I(struct InterfaceType*, Eface, Iface*);
+void	runtime·ifaceE2I(InterfaceType*, Eface, Iface*);
 
 uintptr	runtime·memlimit(void);