[PATCH] PR modula2/120673: Mutually dependent types crash the compiler

This patch fixes an ICE which will occur if cyclic dependent types
are used when declaring a variable.  This patch detects the
cyclic dependency and issues an error message for each outstanding
component.

gcc/m2/ChangeLog:

	PR modula2/120673
	* gm2-compiler/M2GCCDeclare.mod (ErrorDepList): New
	global variable set containing every errant dependency symbol.
	(mystop): Remove.
	(EmitCircularDependancyError): Replace with ...
	(EmitCircularDependencyError): ... this.
	(AssertAllTypesDeclared): Rewrite.
	(DoVariableDeclaration): Ditto.
	(TypeDependentsDeclared): New procedure function.
	(PrepareGCCVarDeclaration): Ditto.
	(DeclareVariable): Remove assert.
	(DeclareLocalVariable): Ditto.
	(Constructor): Initialize ErrorDepList.
	* gm2-compiler/M2MetaError.mod (doErrorScopeProc): Rewrite
	and ensure that a symbol with a module scope does not lookup
	from a definition module.
	* gm2-compiler/P2SymBuild.mod (BuildType): Rewrite so that
	a synonym type is created using the token refering to the name
	on the lhs.

gcc/testsuite/ChangeLog:

	PR modula2/120673
	* gm2/pim/fail/badmodvar.mod: New test.
	* gm2/pim/fail/cyclictypes.mod: New test.
	* gm2/pim/fail/cyclictypes2.mod: New test.
	* gm2/pim/fail/cyclictypes4.mod: New test.

(cherry picked from commit fba2f08152375e2c1c167ec921a0197e4c07efc6)

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