alpha: fix ceil on sNaN input

The alpha version of ceil wrongly return sNaN for sNaN input. Fix that
by checking for NaN and by returning the input value added with itself
in that case.

Finally remove the code to handle inexact exception, ceil should never
generate such an exception.

Changelog:
	* sysdeps/alpha/fpu/s_ceil.c (__ceil): Add argument with itself
	when it is a NaN.
	[_IEEE_FP_INEXACT] Remove.
	* sysdeps/alpha/fpu/s_ceilf.c (__ceilf): Likewise.

(cherry picked from commit 062e53c1)