[PATCH] math: Sync acosh with CORE-MATH 887cab6f

[Paul Zimmermann]

thank you Adhemerval for this patch.

The detailed proof of correctness is available from
https://core-math.gitlabpages.inria.fr/acosh.pdf
(no need to read it to review this patch).

Apart from this proof, this new version fixes some values
that were not correctly rounded, for example 0x1.00a800422847ap+0
with rounding toward zero.

Paul