Include s_sin.c in s_sincos.c

Include s_sin.c in s_sincos.c

Include the __sin and __cos functions as local static copies to allow
deper optimization of the functions.  This change shows an improvement
of about 17% in the min case and 12.5% in the mean case for the sincos
microbenchmark on x86_64.

	* sysdeps/ieee754/dbl-64/s_sin.c (__sin)[IN_SINCOS]: Mark function
	static and don't set or restore rounding.
	(__cos)[IN_SINCOS]: Likewise.
	* sysdeps/ieee754/dbl-64/s_sincos.c: Include s_sin.c.
	(__sincos): Set and restore rounding mode.  Remove check for infinite
	or NaN input.