Allow casts between pointers and literal 0 with any integer type

These were already allowed:
	        0 => ptr
	       0l => ptr, but on 32bit only (matching the pointer size)
	      0ll => ptr, but on 64bit only (matching the pointer size)
	 cbyte(0) => ptr
	cshort(0) => ptr

Additionally, the following are now allowed too:
	       0l => ptr on 64bit
	      0ll => ptr on 32bit
	any 0 ptr => any integer type (opposite direction)

Updating hCalcTypesDiff() (overload resolution) accordingly is not
necessary, because it re-uses the code from ast-node-conv since db40150e.