[llvm] [libc-utils] disable target_compile_features (PR #121883)

[Brian Cain via llvm-commits]

androm3da wrote:

> Ok, so if you're on a Linux host and compiling for a Linux target, I think #114591 is entirely unrelated. You might be getting the CMake top-level CMake complaint, but likely for different reasons.
> 
> What I would try to do is go to your build directory and look at files like `<build>/CMakeFiles/CMakeConfigureLog.yaml`, there's usually information about why configuration checks have failed.

There's no yaml files but there is an error log.  How do I determine which parts are trying to satisfy whatever "no known features" is looking for?

For example -- is it looking for `__cxa_throw` to validate cxx17?  I guess that shouldn't be there because we're bootstrapping, so there's no C++ library yet.  Or is there something else I should be looking for?  [here is the unabridged obj_libs/CMakeFiles/CMakeError.log.gz](https://github.com/user-attachments/files/18444145/CMakeError.log.gz)

```
Determining if the function __cxa_throw exists in the stdc++ failed with the following output:
Change Dir: /local/mnt/workspace/upstream/toolchain_for_hexagon/obj_libs/CMakeFiles/CMakeScratch/TryCompile-dLbtLL

Run Build Command(s):/pkg/qct/software/ninja/1.8.2/ninja cmTC_67227 && [1/2] Building C object CMakeFiles/cmTC_67227.dir/CheckFunctionExists.c.o
[2/2] Linking C executable cmTC_67227
FAILED: cmTC_67227 
: && /local/mnt/workspace/upstream/toolchain_for_hexagon/clang+llvm-20.0.0-cross-hexagon-unknown-linux-musl/x86_64-linux-gnu/bin/hexagon-unknown-linux-musl-clang --target=hexagon-unknown-linux-musl -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -DCHECK_FUNCTION_EXISTS=__cxa_throw  --start-no-unused-arguments --unwindlib=none --end-no-unused-arguments -nostdlib++ -nostdinc++ -nodefaultlibs -Wl,--color-diagnostics CMakeFiles/cmTC_67227.dir/CheckFunctionExists.c.o -o cmTC_67227  -lstdc++  -lc && :
hexagon-unknown-linux-musl-ld.lld: error: unable to find library -lstdc++
hexagon-unknown-linux-musl-clang: error: hexagon-ld command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: subcommand failed.
```


https://github.com/llvm/llvm-project/pull/121883