PR modula2/114422 Attempting to declare a set of unknown type causes ICE

This patch corrects an error message directive which did not
escape the { character.  The patch also contains test cases
to stress set declaration errors.

gcc/m2/ChangeLog:

	PR modula2/114422
	* gm2-compiler/M2Quads.mod (BuildConstructor): Add escape
	character.

gcc/testsuite/ChangeLog:

	PR modula2/114422
	* gm2/iso/fail/badset.mod: New test.
	* gm2/iso/fail/badset2.mod: New test.
	* gm2/iso/fail/badset3.mod: New test.

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