Consolidate input partitioning into do_cos and do_sin

All calls to do_cos are preceded by code that partitions x into a
larger double that gives an offset into the sincos table and a smaller
double that is used in a polynomial computation.  Consolidate all of
them into do_cos and do_sin to reduce code duplication.

	* sysdeps/ieee754/dbl-64/s_sin.c (do_cos): Accept X and DX as input
	arguments.  Consolidate input partitioning from callers here.
	(do_cos_slow): Likewise.
	(do_sin): Likewise.
	(do_sin_slow): Likewise.
	(do_sincos_1): Remove the no longer necessary input partitioning.
	(do_sincos_2): Likewise.
	(__sin): Likewise.
	(__cos): Likewise.
	(slow1): Likewise.
	(slow2): Likewise.
	(sloww1): Likewise.
	(sloww2): Likewise.
	(bsloww1): Likewise.
	(bsloww2): Likewise.
	(cslow2): Likewise.