[libc][math] Added atanhf function.

[orex]

Summary

Performance by core-math (core-math/glibc 2.31/current llvm-14):
10.845/43.174/13.467

The review is done on top of D132809.

[zimmermann6]

ok for me. I get slightly better figures for llvm-libc:

zimmerma@biscotte:~/svn/core-math$ LIBM=/localdisk/zimmerma/llvm-project/build/projects/libc/lib/libllvmlibc.a CORE_MATH_PERF_MODE=rdtsc ./perf.sh atanhf
GNU libc version: 2.34
GNU libc release: stable
23.547
70.432
20.065

This is on a AMD EPYC 7282.

[orex]

Thank you, Paul! I'll land the revision after Tue review.

[lntue]

libc/src/math/generic/atanhf.cpp

22

|x| >= 1.0 ?

[orex]

Fixed comments.

[orex]

Fixed entrypoint.

[orex]

Review fixes.

[lntue]

libc/src/math/generic/CMakeLists.txt

1235

Update this dependency.