re PR c++/71537 (GCC rejects consetxpr boolean conversions and comparisons on the result of pointer arithmetic.)

	PR c++/71537
	* fold-const.c (fold_comparison): Assume CONSTANT_CLASS_P (base0)
	plus offset is non-zero.  For maybe_nonzero_address decl base0,
	require indirect_base0.

	* g++.dg/cpp0x/constexpr-71537.C: New test.

From-SVN: r243286