re PR sanitizer/70342 (g++ -fsanitize=undefined never finishes compiling (>24h) in qtxmlpatterns test suite)

	PR sanitizer/70342
	* fold-const.c (tree_single_nonzero_warnv_p): For TARGET_EXPR, use
	TARGET_EXPR_SLOT as a base.

	* g++.dg/ubsan/null-7.C: New test.

Co-Authored-By: Jakub Jelinek <jakub@redhat.com>

From-SVN: r235637