[libc] [llvm] [libc][math] Refactor frexpf128 implementation to header-only in src/… (PR #147822)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `libc-aarch64-ubuntu-dbg` running on `libc-aarch64-ubuntu` while building `libc,utils` at step 4 "annotate".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/104/builds/26669

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 4 (annotate) failure: 'python ../llvm-zorg/zorg/buildbot/builders/annotated/libc-linux.py ...' (failure)
...
-- Set CPU features: FullFP16
-- Compiler features available: builtin_ceil_floor_rint_trunc;builtin_fmax_fmin;builtin_fmaxf16_fminf16;builtin_round;cfloat128;float128;float16
-- Using getrandom for hashtable randomness
-- check-runtimes does nothing.
-- Configuring done
-- Generating done
-- Build files have been written to: /home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu/build
@@@BUILD_STEP build libc@@@
Running: ninja libc
[1/2] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.frexpf128.dir/frexpf128.cpp.o
FAILED: libc/src/math/generic/CMakeFiles/libc.src.math.generic.frexpf128.dir/frexpf128.cpp.o 
/usr/bin/clang++ -DLIBC_NAMESPACE=__llvm_libc_20_0_0_git -D_DEBUG -I/home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu/llvm-project/libc -isystem libc/include -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wstring-conversion -fdiagnostics-color -g -DLIBC_QSORT_IMPL=LIBC_QSORT_QUICK_SORT -DLIBC_ADD_NULL_CHECKS -DLIBC_ERRNO_MODE=LIBC_ERRNO_MODE_DEFAULT -fpie -fno-builtin -fno-exceptions -fno-lax-vector-conversions -fno-unwind-tables -fno-asynchronous-unwind-tables -fno-rtti -ftrivial-auto-var-init=pattern -fno-omit-frame-pointer -Wall -Wextra -Werror -Wconversion -Wno-sign-conversion -Wdeprecated -Wno-c99-extensions -Wno-gnu-imaginary-constant -Wno-pedantic -Wimplicit-fallthrough -Wwrite-strings -Wextra-semi -Wnewline-eof -Wnonportable-system-include-path -Wstrict-prototypes -Wthread-safety -Wglobal-constructors -DLIBC_COPT_PUBLIC_PACKAGING -std=gnu++17 -MD -MT libc/src/math/generic/CMakeFiles/libc.src.math.generic.frexpf128.dir/frexpf128.cpp.o -MF libc/src/math/generic/CMakeFiles/libc.src.math.generic.frexpf128.dir/frexpf128.cpp.o.d -o libc/src/math/generic/CMakeFiles/libc.src.math.generic.frexpf128.dir/frexpf128.cpp.o -c /home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu/llvm-project/libc/src/math/generic/frexpf128.cpp
In file included from /home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu/llvm-project/libc/src/math/generic/frexpf128.cpp:11:
/home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu/llvm-project/libc/src/__support/math/frexpf128.h:24:27: error: constexpr function never produces a constant expression [-Winvalid-constexpr]
static constexpr float128 frexpf128(float128 x, int *exp) {
                          ^
/home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu/llvm-project/libc/src/__support/math/frexpf128.h:25:10: note: non-constexpr function 'frexp<long double, 0>' cannot be used in a constant expression
  return fputil::frexp(x, *exp);
         ^
/home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu/llvm-project/libc/src/__support/FPUtil/ManipulationFunctions.h:32:15: note: declared here
LIBC_INLINE T frexp(T x, int &exp) {
              ^
1 error generated.
ninja: build stopped: subcommand failed.
['ninja', 'libc'] exited with return code 1.
The build step threw an exception...
Traceback (most recent call last):
  File "../llvm-zorg/zorg/buildbot/builders/annotated/libc-linux.py", line 176, in step
    yield
  File "../llvm-zorg/zorg/buildbot/builders/annotated/libc-linux.py", line 138, in main
    run_command(['ninja', 'libc'])
  File "../llvm-zorg/zorg/buildbot/builders/annotated/libc-linux.py", line 191, in run_command
    util.report_run_cmd(cmd, cwd=directory)
  File "/home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu/llvm-zorg/zorg/buildbot/builders/annotated/util.py", line 49, in report_run_cmd
    subprocess.check_call(cmd, shell=shell, *args, **kwargs)
  File "/usr/lib/python2.7/subprocess.py", line 190, in check_call
    raise CalledProcessError(retcode, cmd)
CalledProcessError: Command '['ninja', 'libc']' returned non-zero exit status 1
@@@STEP_FAILURE@@@
@@@BUILD_STEP libc-unit-tests@@@
Running: ninja libc-unit-tests
[1/1024] Running unit test libc.test.src.math.rintf16_test.__unit__.__NO_ROUND_OPT
[==========] Running 5 tests from 1 test suite.
[ RUN      ] LlvmLibcRIntTest.specialNumbers
[       OK ] LlvmLibcRIntTest.specialNumbers (7 us)
[ RUN      ] LlvmLibcRIntTest.RoundNumbers
[       OK ] LlvmLibcRIntTest.RoundNumbers (65 us)
[ RUN      ] LlvmLibcRIntTest.Fractions
[       OK ] LlvmLibcRIntTest.Fractions (22 us)

```

</details>

https://github.com/llvm/llvm-project/pull/147822