re PR sanitizer/79572 (reference binding to null pointer not reported with -fsanitize...

re PR sanitizer/79572 (reference binding to null pointer not reported with -fsanitize=undefined)

	PR c++/79572
	* c-ubsan.h (ubsan_maybe_instrument_reference): Change argument to
	tree *.
	* c-ubsan.c (ubsan_maybe_instrument_reference): Likewise.  Handle
	not just NOP_EXPR to REFERENCE_TYPE, but also INTEGER_CST with
	REFERENCE_TYPE.

	* cp-gimplify.c (cp_genericize_r): Sanitize INTEGER_CSTs with
	REFERENCE_TYPE.  Adjust ubsan_maybe_instrument_reference caller
	for NOP_EXPR to REFERENCE_TYPE.

	* g++.dg/ubsan/null-8.C: New test.

From-SVN: r246621