c: [PR104506] Fix ICE after error due to change of type to error_mark_node

c: [PR104506] Fix ICE after error due to change of type to error_mark_node

The problem here is we end up with an error_mark_node when calling
useless_type_conversion_p and that ICEs. STRIP_NOPS/tree_nop_conversion
has had a check for the inner type being an error_mark_node since g9a6bb3f78c96
(2000). This just adds the check also to tree_ssa_useless_type_conversion.
STRIP_USELESS_TYPE_CONVERSION is mostly used inside the gimplifier
and the places where it is used outside of the gimplifier would not
be adding too much overhead.

OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

Thanks,
Andrew Pinski

	PR c/104506

gcc/ChangeLog:

	* tree-ssa.cc (tree_ssa_useless_type_conversion):
	Check the inner type before calling useless_type_conversion_p.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr104506-1.c: New test.
	* gcc.dg/pr104506-2.c: New test.
	* gcc.dg/pr104506-3.c: New test.