math: Sync atanh from CORE-MATH

math: Sync atanh from CORE-MATH

The CORE-MATH commit dc9465e7 fixes some issues:

Failure: Test: atanh_towardzero (0x8.3f79103b3c64p-4)
Result:
 is:          5.7018661316561103e-01   0x1.23ef7ff0539c6p-1
 should be:   5.7018661316561092e-01   0x1.23ef7ff0539c5p-1
 difference:  1.1102230246251565e-16   0x1.0000000000000p-53
 ulp       :  1.0000
 max.ulp   :  0.0000
Failure: Test: atanh_towardzero (0x8.3f7d95aabaf7p-4)
Result:
 is:          5.7019248543911060e-01   0x1.23f044fac5997p-1
 should be:   5.7019248543911049e-01   0x1.23f044fac5996p-1
 difference:  1.1102230246251565e-16   0x1.0000000000000p-53
 ulp       :  1.0000
 max.ulp   :  0.0000
Failure: Test: atanh_towardzero (0x8.3f805380d6728p-4)
Result:
 is:          5.7019604623795527e-01   0x1.23f0bc75cd113p-1
 should be:   5.7019604623795516e-01   0x1.23f0bc75cd112p-1
 difference:  1.1102230246251565e-16   0x1.0000000000000p-53
 ulp       :  1.0000
 max.ulp   :  0.0000
Maximal error of `atanh_towardzero'
 is      : 1 ulp
 accepted: 0 ulp

Checked on x86_64-linux-gnu, x86_64-linux-gnu-v3, aarch64-linux-gnu,
and i686-linux-gnu.