Merge bitcoin/bitcoin#25808: fs: work around u8path deprecated-declaration warnings with libc++

ced00f5a2e2b8623d1ee6a9afef80fc5df08d509 fs: work around u8path deprecated-declaration warnings with libc++ (fanquake)

Pull request description:

  When building in c++20 mode using libc++, the following warning is emitted:
  ```bash
  ./fs.h:72:29: warning: 'u8path<std::string>' is deprecated [-Wdeprecated-declarations]
      return std::filesystem::u8path(utf8_str);
                              ^
  /usr/lib/llvm-14/bin/../include/c++/v1/__filesystem/u8path.h:72:27: note: 'u8path<std::string>' has been explicitly marked deprecated here
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_DEPRECATED_WITH_CHAR8_T
                            ^
  /usr/lib/llvm-14/bin/../include/c++/v1/__config:1042:43: note: expanded from macro '_LIBCPP_DEPRECATED_WITH_CHAR8_T'
                                            ^
  /usr/lib/llvm-14/bin/../include/c++/v1/__config:1007:48: note: expanded from macro '_LIBCPP_DEPRECATED'
                                                 ^
  1 warning generated.
  ```

  as [`u8path<std::string>`](https://en.cppreference.com/w/cpp/filesystem/path/u8path) is deprecated starting with C++20.

  Fixes: #24682.

ACKs for top commit:
  MarcoFalke:
    review ACK ced00f5a2e2b8623d1ee6a9afef80fc5df08d509
  hebasto:
    ACK ced00f5a2e2b8623d1ee6a9afef80fc5df08d509

Tree-SHA512: f012c4f0bec691090eb3ff128ee0cdc392f73e7857b97131da924ab18c088a82d2fba95316d405feb8b744cba63bfeff7b08143086c173fddbf972139ea0ac0b

0 files changed, 0 insertions, 0 deletions