Undefined reference to `ShowWindow@16'

I really hope I'm not repeating anything here (having tried to find an answer via 'search'), but...

I recently updated to 1.28 and at same time uninstalled my old MinGW and installed 5.1.3. I then did a Synchronize Modules, and Rebuild All Modules. Using some code from the forums to create a borderless window, I am trying to compile this [extract]:

SuperStrict

Extern "win32"
   Function GetActiveWindow:Int()
   Function ShowWindow:Int(hWnd:Int,nCmdShow:Int)
EndExtern

Graphics 320,106

Local wHandle:Long=GetActiveWindow()
ShowWindow(wHandle,SW_MINIMIZE)
...

but get an "undefined reference to `ShowWindow@16'" compiler error. Can anyone please tell me what I'm doing wrong?

Don't worry - having just discovered that the defs for GetActiveWindow and ShowWindow are already in user32.bmx, I deleted the Extern block and it compiled fine... Makes me wonder though - how can you tell which API functions are already in the mods and which need defining via an Extern block?

GREP for it in mod/pub.mod/win32.mod ;)