Added: AppleClang CMake support

[kasperhbo]

Update: Cmake to CMAKE Target 23
Fixed: Linking errors, one er two spdlog calls.
Removed: #ifdef IMTERM_USE_FMT no just use fmt

[starlight-traveler]

What version of the spdlog are you using to compile? Current submodule seems to have a linker error with CLANG 23, here is a snippet of that:

/Users/foo/Documents/Projects/C/GUI/ImTerm/example/external/spdlog/include/spdlog/fmt/bundled/core.h:202:20: error: no template named 'result_of' in namespace 'std'; did you mean '::fmt::internal::result_of'?
typedef typename std::result_of<
^~~~~
/Users/foo/Documents/Projects/C/GUI/ImTerm/example/external/spdlog/include/spdlog/fmt/bundled/core.h:197:8: note: '::fmt::internal::result_of' declared here
struct result_of;

The error is in the spdlog library, but which branch/which commit is being used?