modula2: Narrow subranges to int or unsigned int if ZTYPE is the base type.

This patch narrows the subrange base type to INTEGER or CARDINAL
providing the range is satisfied.  It only does this when the subrange
base type is the ZTYPE.

gcc/m2/ChangeLog:

	* gm2-compiler/M2GCCDeclare.mod (DeclareSubrange): Check
	the base type of the subrange against the ZTYPE and call
	DeclareSubrangeNarrow if necessary.
	(DeclareSubrangeNarrow): New procedure function.

Signed-off-by: Gaius Mulley <gaiusmod2@gmail.com>