libs/libcxx: port for Infineon TASKING compiler.

[v-zhangxiaomeng5]

Exclude cpp files beyong c++14 e.g. filesystem/, ryu/, variant.cpp etc.

Note: Please adhere to Contributing Guidelines.

Summary

Update libcxx/CMakeLists.txt to support Infineon TASKING compiler(supports up to c++14).

Impact

non-TASKING users will not be impacted.

Testing

CI test.

[xiaoxiang781216]

@v-zhangxiaomeng5 please fix:

../nuttx/tools/checkpatch.sh -c -u -m -g 51bcec53c4f166d9fd07b02418491355b9463e1d..HEAD
❌ Commit subject missing colon (e.g. 'subsystem: msg')
Used config files:
    1: .codespellrc
Some checks failed. For contributing guidelines, see:
  https://github.com/apache/nuttx/blob/master/CONTRIBUTING.md

[Barto22]

I'm currently adding support for latest libcxx and libcxxabi, please look at this:
#17826 If you have any suggestions and if you can check my port on Infineon and something will not work I will add fixes.

[xiaoxiang781216]

I'm currently adding support for latest libcxx and libcxxabi, please look at this: #17826 If you have any suggestions and if you can check my port on Infineon and something will not work I will add fixes.

@Barto22 it's unfortunate that Tasking Infineon compiler just support c++14:(.