PR modula2/115804 ICE during gimplification with new isfinite optab

The calls to five m2 builtins have the incorrect return type.
This was detected when adding isfinitedf2 optab to the s390
backend which results in ICEs during gimplification in the
gm2 testsuite.

gcc/m2/ChangeLog:

	PR modula2/115804
	* gm2-gcc/m2builtins.cc (builtin_function_entry): Add GTY.
	(DoBuiltinMemCopy): Add rettype and use rettype in the call.
	(DoBuiltinAlloca): Ditto.
	(DoBuiltinIsfinite): Ditto.
	(DoBuiltinIsnan): Ditto.
	(m2builtins_BuiltInHugeVal): Ditto.
	(m2builtins_BuiltInHugeValShort): Ditto.
	(m2builtins_BuiltInHugeValLong): Ditto.

Co-Authored-By: Stefan Schulze Frielinghaus <stefansf@linux.ibm.com>
Co-Authored-By: Andrew Pinski <quic_apinski@quicinc.com>

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