This is a part of #97655.

Reverts llvm/llvm-project#98075

bots are broken

This is a part of #97655.

This is step 4 of
https://discourse.llvm.org/t/rfc-customizable-namespace-to-allow-testing-the-libc-when-the-system-libc-is-also-llvms-libc/73079

Optimize the core part of `tanhf` implementation that is to compute `e^x`
similar to https://reviews.llvm.org/D133870.  Factor the constants and
polynomial approximation out so that it can be used for `exp10f`

Performance benchmark using perf tool from the CORE-MATH project on Ryzen 1700:
```
$ CORE_MATH_PERF_MODE="rdtsc" ./perf.sh tanhf
GNU libc version: 2.35
GNU libc release: stable
CORE-MATH reciprocal throughput   : 13.377
System LIBC reciprocal throughput : 55.046

BEFORE:
LIBC reciprocal throughput        : 75.674
LIBC reciprocal throughput        : 33.242    (with `-msse4.2` flag)
LIBC reciprocal throughput        : 25.927    (with `-mfma` flag)

AFTER:
LIBC reciprocal throughput        : 26.359
LIBC reciprocal throughput        : 18.888    (with `-msse4.2` flag)
LIBC reciprocal throughput        : 14.243    (with `-mfma` flag)

$ CORE_MATH_PERF_MODE="rdtsc" ./perf.sh tanhf --latency
GNU libc version: 2.35
GNU libc release: stable
CORE-MATH latency   : 43.365
System LIBC latency : 123.499

BEFORE
LIBC latency        : 112.968
LIBC latency        : 104.908   (with `-msse4.2` flag)
LIBC latency        : 92.310    (with `-mfma` flag)

AFTER
LIBC latency        : 69.828
LIBC latency        : 63.874    (with `-msse4.2` flag)
LIBC latency        : 57.427    (with `-mfma` flag)
```

Reviewed By: orex, zimmermann6

Differential Revision: https://reviews.llvm.org/D134002

1) `double log2_eval(double)` function added with better than float precision is added.
2) Some refactoring done to put all auxiliary functions and corresponding data
to one place to reuse the code.
3) Added tests for new functions.
4) Performance and precision tests of the function shows, that it more precise than exiting log2,
(no exceptional cases), but timing is ~5% higer that on current one.

Differential Revision: https://reviews.llvm.org/D132809