PR modula2/117555: Add missing return statement after raise

PR modula2/117555: Add missing return statement after raise

This patch adds missing return statements after a call to RAISE.  Four
of the modules in libgm2 have procedure functions with missing return
statements.  These errors were exposed after the reimplementation of
parameter declaration patch and triggered by -Wreturn-type.  The patch
also adds exit statements to the M2RTS noreturn functions.

gcc/m2/ChangeLog:

	PR modula2/117555
	* gm2-libs-iso/EXCEPTIONS.mod (CurrentNumber): Add return
	statement.
	* gm2-libs-iso/IOChan.mod (ReadResult): Ditto.
	(CurrentFlags): Ditto.
	(DeviceError): Ditto.
	* gm2-libs-iso/IOLink.mod (DeviceTablePtrValue): Ditto.
	* gm2-libs-iso/LongConv.mod (ValueReal): Ditto.
	* gm2-libs/M2RTS.mod (Halt): Add noreturn attribute.
	Add exit (1).
	(HaltC): Add exit (1).
	* pge-boot/GM2RTS.cc (M2RTS_Halt): Add exit (1).
	(M2RTS_HaltC): Ditto.

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