re PR tree-optimization/93156 (abused nonnull attribute evokes new segfault in gcc 10 since Nov 4 commit, 0fb958ab8aa)

	PR tree-optimization/93156
	* tree-ssa-ccp.c (bit_value_binop): For x * x note that the second
	least significant bit is always clear.

	* gcc.dg/tree-ssa/pr93156.c: New test.

From-SVN: r279951