d: Fix ICE in setValue, at d/dmd/dinterpret.c:7013

d: Fix ICE in setValue, at d/dmd/dinterpret.c:7013

Backports ICE fix from upstream.  When casting null to integer or real,
instead of painting the type on the NullExp, we emplace an
IntegerExp/RealExp with the value zero.  Same as when casting from
NullExp to bool.

Reviewed-on: https://github.com/dlang/dmd/pull/13172

	PR d/110511

gcc/d/ChangeLog:

	* dmd/dinterpret.c (Interpreter::visit (CastExp *)): Handle casting
	null to int or float.

gcc/testsuite/ChangeLog:

	* gdc.test/compilable/test21794.d: New test.

(cherry picked from commit 066385c918485d4cef5c243d3b0691193df382de)