re PR c/69835 (-Wnonnull diagnoses parameter comparisons with NULL even when those could have changed)

	PR c/69835
	* common.opt (Wnonnull-compare): New warning.
	* doc/invoke.texi (-Wnonnull): Remove text about comparison
	of arguments against NULL.
	(-Wnonnull-compare): Document.
	* Makefile.in (OBJS): Add gimple-ssa-nonnull-compare.o.
	* tree-pass.h (make_pass_warn_nonnull_compare): Declare.
	* passes.def (pass_warn_nonnull_compare): Add.
	* gimple-ssa-nonnull-compare.c: New file.
c-family/
	* c.opt (Wnonnull-compare): Enable for -Wall.
c/
	* c-typeck.c (build_binary_op): Revert 2015-09-09 change.
cp/
	* typeck.c (cp_build_binary_op): Revert 2015-09-09 change.
testsuite/
	* c-c++-common/nonnull-1.c: Use -Wnonnull-compare instead of
	-Wnonnull in dg-options.
	* c-c++-common/nonnull-2.c: New test.

From-SVN: r233472