Updated CMake build to compile in C++17 mode if available

[johnplatts]

Updated CMakeLists.txt to build libjxl in C++17 mode if supported by the C++ compiler.

For optimal dynamic dispatch with Google Highway, Clang 5 or later, GCC 7 or later, or MSVC 19.16 or later is needed, and all of these compilers have support for the C++17 standard.

Also added workarounds to suppress any -Wdeprecated-declarations warning that might be emitted by std::stable_sort with GCC or Clang in C++17 mode due to the libstdc++ implementation of std::stable_sort using std::get_temporary_buffer, which has been deprecated in C++17.

[eustas]

I'll also file an issue to get rid of stable_sort at some moment.

Thanks.