PR modula2/117371: type incompatibility between INTEGER and CARDINAL

This patch enforces a const expression increment in a FOR loop.
It also fixes missing error locations.  The FOR loop last iterator
value is now calculated during M2GenGCC after all types and constants have
been resolved.  This results in fewer quadruples (as there is no need to
build two paths for step > 0 and step < 0).

gcc/m2/ChangeLog:

	PR modula2/117371
	* gm2-compiler/M2Base.mod (MixMetaTypes): Add parameter TRUE to
	MetaErrorDecl.
	(IsUserType): Test against ZType.
	(MixTypesDecl): Test for ZType.
	* gm2-compiler/M2GenGCC.mod (ErrorMessageDecl): Add parameter TRUE to
	MetaErrorDecl.
	(CodeLastForIterator): New procedure.
	(FoldLastForIterator): Ditto.
	(PerformLastForIterator): Ditto.
	(CodeStatement): Add case clause for LastForIteratorOp.
	(ErrorMessageDecl): Add iserror parameter.
	Call MetaErrorDecl with iserror parameter.
	(checkIncorrectMeta): Call MetaErrorDecl with TRUE parameter.
	(CheckBinaryExpressionTypes): Ditto.
	(CheckElementSetTypes): Ditto.
	* gm2-compiler/M2LexBuf.def (MakeVirtualTok): Update comment
	detailing the fall back when UnknownTokenNo is encountered.
	(MakeVirtual2Tok): Ditto.
	* gm2-compiler/M2LexBuf.mod (MakeVirtualTok): Check against
	UnknownTokenNo.
	(MakeVirtual2Tok): Ditto.
	* gm2-compiler/M2MetaError.def (MetaErrorDecl): Add error parameter.
	* gm2-compiler/M2MetaError.mod (MetaErrorDecl): Add error
	parameter.
	Issue warning if error is FALSE.
	* gm2-compiler/M2Quads.def (QuadOperator): Add LastForIteratorOp.
	* gm2-compiler/M2Quads.mod (AddQuadInformation): New case clause
	LastForIteratorOp.
	(CheckAddTuple2Read): New procedure.
	(BuildForLoopToRangeCheck): Remove.
	(ForLoopLastIteratorVariable): Ditto.
	(ForLoopLastIteratorConstant): Ditto.
	(ForLoopLastIterator): Reimplement.
	(BuildForToByDo): Remove ByType from call to ForLoopLastIterator.
	(WriteQuad): New case clause LastForIteratorOp.
	(WriteOperator): Ditto.
	* gm2-compiler/M2Students.def
	(CheckForVariableThatLooksLikeKeyword): Replace with ...
	(CheckVariableAgainstKeyword): ... this.
	* gm2-compiler/M2Students.mod
	(CheckForVariableThatLooksLikeKeyword): Replace with ...
	(CheckVariableAgainstKeyword): ... this.
	* gm2-compiler/M2SymInit.mod (CheckLastForIterator): New
	procedure.
	(CheckReadBeforeInitQuad): New case clause to call
	CheckLastForIterator.
	* gm2-compiler/P2SymBuild.mod: Replace
	CheckForVariableThatLooksLikeKeyword with CheckVariableAgainstKeyword.

gcc/testsuite/ChangeLog:

	PR modula2/117371
	* gm2/iso/fail/forloopbyvar.mod: New test.
	* gm2/iso/fail/forloopbyvar4.mod: New test.
	* gm2/iso/fail/forloopbyvar5.mod: New test.
	* gm2/iso/pass/forloopbyvar3.mod: New test.

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