Add support for tailcalls from internal C functions.

PPC: Fix __call metamethod for tailcalls.

src/lj_api.c

@@ -1104,7 +1104,7 @@ LUA_API int lua_yield(lua_State *L, int nresults)
       setcont(top+1, lj_cont_hook);
       setframe_pc(top+1, cframe_pc(cf)-1);
       setframe_gc(top+2, obj2gco(L));
-      top[2].fr.tp.ftsz = (int)((char *)(top+3)-(char *)L->base)+FRAME_CONT;
+      setframe_ftsz(top+2, (int)((char *)(top+3)-(char *)L->base)+FRAME_CONT);
       L->top = L->base = top+3;
     }
 #if LJ_TARGET_X64