Bugfix detect assigning constant constructors within a code block.

Bugfix detect assigning constant constructors within a code block.

gcc/m2/ChangeLog:

	* gm2-compiler/M2Quads.def (BuildAssignConstant):
	Exported.
	* gm2-compiler/M2Quads.mod (BuildAssignConstant): New
	procedure.  (BuildAssignment) check whether designator
	is a constant and generate an error.
	* gm2-compiler/P3Build.bnf: Call BuildAssignConstant
	during ConstStatement.  Pass tokenno down to constant
	constructor parameters.
	* gm2-compiler/PHBuild.bnf: Call BuildAssignConstant
	during ConstStatement.

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