XCode 15 (on Ventura and Sonoma) has a linker issue, see https://github.com/mesonbuild/meson/issues/12282, workaround is to use ld_classic

Also enforce the path to x86-64 GCC.

- add proper detection of Boost
- add logic for making FlexLexer.h always available
- statically link the executable if prefer_static=true
- add Homebrew native file
- add Windows cross file