* Bring the wx frontend more in-line with the rest of the codebase.
* Always default to Unicode APIs on Windows.
* Clean up all include guards and headers.
* Use add_compile_definitions everywhere.
* Remove unused intermediate target.
* Add ASAN support for MSVC.
* Remove duplicate option definitions.
* Configure MinGW separately from the toolchain
* Move toolchain-specific options to their own files.
* Clean up and modernize the use of toolchain options.
* Use modern cmake LTO support.
* Remove dead cmake code and cmake functions available in upstream cmake.
* Update README.md to remove references to removed build options.
Fabrice de Gans