[Bug] Builds using GCC 16.0.1 fail on u8string() usage

[oznogon]

Fedora 44 updates the GNU toolchain from gcc 15.2 to gcc 16.0.1. This causes build failures on master using F44 citing no known conversion for argument 1 from ‘std::u8string’, when it builds without issue on F43.

/home/username/git/daid/emptyepsilon-compile/EmptyEpsilon/src/packResourceProvider.cpp:95:87: error: no matching function for call to ‘string::string(<brace-enclosed initializer list>)’
   95 |             if (!entry.is_directory() && string { entry.path().extension().u8string() }.lower() == ".pack")
      |                                                                                       ^
  • there are 11 candidates
In file included from /home/username/git/daid/emptyepsilon-compile/SeriousProton/src/resources.h:4,
                 from /home/username/git/daid/emptyepsilon-compile/EmptyEpsilon/src/packResourceProvider.h:4,
                 from /home/username/git/daid/emptyepsilon-compile/EmptyEpsilon/src/packResourceProvider.cpp:1:
    • candidate 1: ‘string::string(float, int)’
      /home/username/git/daid/emptyepsilon-compile/SeriousProton/src/stringImproved.h:47:5:
         47 |     string(const float nr, int decimals = 2) : std::string()
            |     ^~~~~~
      • no known conversion for argument 1 from ‘std::u8string’ {aka ‘std::__cxx11::basic_string<char8_t>’} to ‘float’
        /home/username/git/daid/emptyepsilon-compile/SeriousProton/src/stringImproved.h:47:24:
           47 |     string(const float nr, int decimals = 2) : std::string()
              |            ~~~~~~~~~~~~^~
    • candidate 2: ‘string::string(unsigned int)’
      /home/username/git/daid/emptyepsilon-compile/SeriousProton/src/stringImproved.h:40:5:
         40 |     string(const unsigned int nr) : std::string()
            |     ^~~~~~
      • no known conversion for argument 1 from ‘std::u8string’ {aka ‘std::__cxx11::basic_string<char8_t>’} to ‘unsigned int’
        /home/username/git/daid/emptyepsilon-compile/SeriousProton/src/stringImproved.h:40:31:
           40 |     string(const unsigned int nr) : std::string()
              |            ~~~~~~~~~~~~~~~~~~~^~
...

This appears to be related to C++20 changes: ToruNiina/toml11#104

GCC 16 changes the default language version from gnu++17 to gnu++20.

• Replacing u8string() and generic_u8string() calls with string() and generic_string() in EmptyEpsilon packResourceProvider.cpp and SeriousProton resources.cpp silences the errors, but it's unclear if those changes would affect cross-platform compatibility.
• Specifying -std=gnu++17 via CMake target_compile_options in both EmptyEpsilon and SeriousProton also silences the errors.