[libc] Mass replace enclosing namespace (#67032)

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

[libc][math] Clean up exhaustive tests implementations.

Clean up exhaustive tests. Let check functions return number of failures instead of passed/failed.

Reviewed By: sivachandra

Differential Re

[libc][math] Clean up exhaustive tests implementations.

Clean up exhaustive tests. Let check functions return number of failures instead of passed/failed.

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D153682

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[libc] Enable hermetic floating point tests again.

Fixing an issue with LLVM libc's fenv.h defined rounding mode macros
differently from system libc, making get_round() return different values from

[libc] Enable hermetic floating point tests again.

Fixing an issue with LLVM libc's fenv.h defined rounding mode macros
differently from system libc, making get_round() return different values from
fegetround(). Also letting math tests to skip rounding modes that cannot be
set. This should allow math tests to be run on platforms in which fenv.h is not
implemented yet.

This allows us to re-enable hermatic floating point tests in
https://reviews.llvm.org/D151123 and reverting https://reviews.llvm.org/D152742.

Reviewed By: jhuber6

Differential Revision: https://reviews.llvm.org/D152873

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[libc] Enable custom logging in LibcTest

This patch mimics the behavior of Google Test and allow users to log custom messages after all flavors of ASSERT_ / EXPECT_.

Reviewed By: sivachandra, lntue

[libc] Enable custom logging in LibcTest

This patch mimics the behavior of Google Test and allow users to log custom messages after all flavors of ASSERT_ / EXPECT_.

Reviewed By: sivachandra, lntue

Differential Revision: https://reviews.llvm.org/D152630

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[libc][NFC] Move UnitTest and IntegrationTest to the 'test' directory.

This part of the effort to make all test related pieces into the `test`
directory. This helps is excluding test related pieces

[libc][NFC] Move UnitTest and IntegrationTest to the 'test' directory.

This part of the effort to make all test related pieces into the `test`
directory. This helps is excluding test related pieces in a straight
forward manner if LLVM_INCLUDE_TESTS is OFF. Future patches will also move
the MPFR wrapper and testutils into the 'test' directory.

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[libc] Implement tanf function correctly rounded for all rounding modes.

Implement tanf function correctly rounded for all rounding modes.

We use the range reduction that is shared with `sinf`, `co

[libc] Implement tanf function correctly rounded for all rounding modes.

Implement tanf function correctly rounded for all rounding modes.

We use the range reduction that is shared with `sinf`, `cosf`, and `sincosf`:
```
k = round(x * 32/pi) and y = x * (32/pi) - k.
```
Then we use the tangent of sum formula:
```
tan(x) = tan((k + y)* pi/32) = tan((k mod 32) * pi / 32 + y * pi/32)
= (tan((k mod 32) * pi/32) + tan(y * pi/32)) / (1 - tan((k mod 32) * pi/32) * tan(y * pi/32))
```
We need to make a further reduction when `k mod 32 >= 16` due to the pole at `pi/2` of `tan(x)` function:
```
if (k mod 32 >= 16): k = k - 31, y = y - 1.0
```
And to compute the final result, we store `tan(k * pi/32)` for `k = -15..15` in a table of 32 double values,
and evaluate `tan(y * pi/32)` with a degree-11 minimax odd polynomial generated by Sollya with:
```
> P = fpminimax(tan(y * pi/32)/y, [|0, 2, 4, 6, 8, 10|], [|D...|], [0, 1.5]);
```

Performance benchmark using `perf` tool from the CORE-MATH project on Ryzen 1700:
```
$ CORE_MATH_PERF_MODE="rdtsc" ./perf.sh tanf
CORE-MATH reciprocal throughput : 18.586
System LIBC reciprocal throughput : 50.068

LIBC reciprocal throughput : 33.823
LIBC reciprocal throughput : 25.161 (with `-msse4.2` flag)
LIBC reciprocal throughput : 19.157 (with `-mfma` flag)

$ CORE_MATH_PERF_MODE="rdtsc" ./perf.sh tanf --latency
GNU libc version: 2.31
GNU libc release: stable
CORE-MATH latency : 55.630
System LIBC latency : 106.264

LIBC latency : 96.060
LIBC latency : 90.727 (with `-msse4.2` flag)
LIBC latency : 82.361 (with `-mfma` flag)
```

Reviewed By: orex

Differential Revision: https://reviews.llvm.org/D131715

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