const runtime.heapArenaWords

3 uses

	runtime (current package)
		malloc.go#L250: 	heapArenaWords = heapArenaBytes / goarch.PtrSize
		malloc.go#L258: 	heapArenaBitmapWords = heapArenaWords / (8 * goarch.PtrSize)
		mbitmap.go#L416: 	word := addr / goarch.PtrSize % heapArenaWords