Use libm_alias_double for alpha.

Use libm_alias_double for alpha.

Continuing the preparation for additional _FloatN / _FloatNx function
aliases, this patch makes alpha libm function implementations use
libm_alias_double to define function aliases.  This also simplifies
the code because the compatibility for long double = double is handled
by libm_alias_double instead of locally in each source file.

Tested with build-many-glibcs.py for alpha-linux-gnu that installed
stripped shared libraries are unchanged by the patch.

	* sysdeps/alpha/fpu/s_ceil.c: Include <libm-alias-double.h>.
	(ceil): Define using libm_alias_double.
	* sysdeps/alpha/fpu/s_copysign.c: Include <libm-alias-double.h>.
	(copysign): Define using libm_alias_double.
	* sysdeps/alpha/fpu/s_fabs.c: Include <libm-alias-double.h>.
	(fabs): Define using libm_alias_double.
	* sysdeps/alpha/fpu/s_floor.c: Include <libm-alias-double.h>.
	(floor): Define using libm_alias_double.
	* sysdeps/alpha/fpu/s_fmax.S: Include <libm-alias-double.h>.
	(fmax): Define using libm_alias_double.
	* sysdeps/alpha/fpu/s_fmin.S: Include <libm-alias-double.h>.
	(fmin): Define using libm_alias_double.
	* sysdeps/alpha/fpu/s_lrint.c: Include <libm-alias-double.h>.
	(lrint): Define using libm_alias_double.
	(llrint): Likewise.
	* sysdeps/alpha/fpu/s_lround.c: Include <libm-alias-double.h>.
	(lround): Define using libm_alias_double.
	(llround): Likewise.
	* sysdeps/alpha/fpu/s_rint.c: Include <libm-alias-double.h>.
	(rint): Define using libm_alias_double.
	* sysdeps/alpha/fpu/s_trunc.c: Include <libm-alias-double.h>.
	(trunc): Define using libm_alias_double.