pre-integration of CORE-MATH routines

[Paul Zimmermann]

       Hi,

Saban Houssein (in cc) did a pre-integration of all binary64 CORE-MATH
functions into GNU libc, and all remaining binary32 functions.

The corresponding patches are available from the CORE-MATH page:

https://core-math.gitlabpages.inria.fr/

for example for acos:

https://github.com/sbnh1/glibc/tree/acos

This pre-integration work consisted in:

1) replace the GNU libc code by the CORE-MATH code
   (for generic implementations like rsqrt, Saban had to create a specific
   implementation for the target format).

2) check the GNU libc test suite (make check subdirs=math) works,
   and fix any issues into CORE-MATH. There were several issues
   related to spurious/missing underflow, overflow, inexact.

3) check the CORE-MATH test suite works with the patched GNU libc,
   i.e., all inputs are correctly rounded.

After the 2.42 release, anybody interested is welcome to submit patches
based on this pre-integration.

Paul Zimmermann