[compiler-rt] [compiler-rt][builtins] Fix FLOAT16 feature detection (PR #69842)

[via llvm-commits]

littlewu2508 wrote:

> @littlewu2508 What build configurations have you tested this with?

Gentoo is building compiler-rt as a standalone project. The invoked cmake command on my machine is:

```bash
cmake -C /run/user/18014/portage/sys-libs/compiler-rt-17.0.4/work/compiler-rt-17.0.4_build/gentoo_common_config.cmake -G Ninja -DCMAKE_INSTALL_PREFIX=/opt/gentoo/usr -DCOMPILER_RT_INSTALL_PATH=/opt/gentoo/usr/lib/clang/17 -DCOMPILER_RT_INCLUDE_TESTS=no -DCOMPILER_RT_BUILD_LIBFUZZER=OFF -DCOMPILER_RT_BUILD_MEMPROF=OFF -DCOMPILER_RT_BUILD_ORC=OFF -DCOMPILER_RT_BUILD_PROFILE=OFF -DCOMPILER_RT_BUILD_SANITIZERS=OFF -DCOMPILER_RT_BUILD_XRAY=OFF -DPython3_EXECUTABLE=/opt/gentoo/usr/bin/python3.12 -DCAN_TARGET_i386=no -DCAN_TARGET_x86_64=yes -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_TOOLCHAIN_FILE=/run/user/18014/portage/sys-libs/compiler-rt-17.0.4/work/compiler-rt-17.0.4_build/gentoo_toolchain.cmake /run/user/18014/portage/sys-libs/compiler-rt-17.0.4/work/compiler-rt
```

And 

`gentoo_common_config.cmake` is 

```cmake
set(CMAKE_GENTOO_BUILD ON CACHE BOOL "Indicate Gentoo package build")
set(LIB_SUFFIX 64 CACHE STRING "library path suffix" FORCE)
set(CMAKE_INSTALL_LIBDIR lib64 CACHE PATH "Output directory for libraries")
set(CMAKE_INSTALL_INFODIR "/opt/gentoo/usr/share/info" CACHE PATH "")
set(CMAKE_INSTALL_MANDIR "/opt/gentoo/usr/share/man" CACHE PATH "")
set(CMAKE_USER_MAKE_RULES_OVERRIDE "/run/user/18014/portage/sys-libs/compiler-rt-17.0.4/work/compiler-rt-17.0.4_build/gentoo_rules.cmake" CACHE FILEPATH "Gentoo override rules")
set(CMAKE_INSTALL_DOCDIR "/opt/gentoo/usr/share/doc/compiler-rt-17.0.4" CACHE PATH "")
set(BUILD_SHARED_LIBS ON CACHE BOOL "")
set(Python3_FIND_UNVERSIONED_NAMES FIRST CACHE STRING "")
set(CMAKE_INSTALL_ALWAYS 1)
set(CMAKE_ASM_FLAGS_RELWITHDEBINFO "" CACHE STRING "")
set(CMAKE_ASM-ATT_FLAGS_RELWITHDEBINFO "" CACHE STRING "")
set(CMAKE_C_FLAGS_RELWITHDEBINFO "" CACHE STRING "")
set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "" CACHE STRING "")
set(CMAKE_Fortran_FLAGS_RELWITHDEBINFO "" CACHE STRING "")
set(CMAKE_EXE_LINKER_FLAGS_RELWITHDEBINFO "" CACHE STRING "")
set(CMAKE_MODULE_LINKER_FLAGS_RELWITHDEBINFO "" CACHE STRING "")
set(CMAKE_SHARED_LINKER_FLAGS_RELWITHDEBINFO "" CACHE STRING "")
set(CMAKE_STATIC_LINKER_FLAGS_RELWITHDEBINFO "" CACHE STRING "")
```

while `gentoo_toolchain.cmake` is

```cmake
set(CMAKE_ASM_COMPILER "x86_64-pc-linux-gnu-clang")
set(CMAKE_ASM-ATT_COMPILER "x86_64-pc-linux-gnu-clang")
set(CMAKE_C_COMPILER "x86_64-pc-linux-gnu-clang")
set(CMAKE_CXX_COMPILER "x86_64-pc-linux-gnu-clang++")
set(CMAKE_Fortran_COMPILER "x86_64-pc-linux-gnu-gfortran")
set(CMAKE_AR /opt/gentoo/usr/bin/x86_64-pc-linux-gnu-ar CACHE FILEPATH "Archive manager" FORCE)
set(CMAKE_RANLIB /opt/gentoo/usr/bin/x86_64-pc-linux-gnu-ranlib CACHE FILEPATH "Archive index generator" FORCE)
set(CMAKE_SYSTEM_PROCESSOR "x86_64")
```

https://github.com/llvm/llvm-project/pull/69842