re PR c++/68508 (Internal compiler error with parentheses around return value in C++14 with ASan enabled)

	PR c++/68508
	* cp-tree.h (cp_ubsan_maybe_instrument_downcast): Add INTYPE argument.
	* cp-ubsan.c (cp_ubsan_maybe_instrument_downcast): Likewise.  Use
	it instead of or in addition to TREE_TYPE (op).  Use
	is_properly_derived_from, return NULL_TREE if TREE_TYPE (intype) and
	TREE_TYPE (type) are the same type minus qualifiers.
	* typeck.c (build_static_cast_1): Adjust callers.

	* g++.dg/ubsan/pr68508.C: New test.

From-SVN: r230928