Minor optimisations in operator new(size_t, align_val_t)

Minor optimisations in operator new(size_t, align_val_t)

	* libsupc++/new_opa.cc (operator new(size_t, align_val_t)): Use
	__is_pow2 to check for valid alignment. Avoid branching when rounding
	size to multiple of alignment.

From-SVN: r263515