Make llvm-mingw cross-compilation work
Currently meson function checks fail for some functions with llvm-mingw due to compiler builtins. (And if I remember correctly, for some similar reason with gcc too)
For the function detection bugs see MESON#3740, MESON#3676, MESON#3672.
Another blocking issue is that add_project_link_arguments
adds arguments to native compiler and cross compiler MESON#3669.
A relatively trivial but worth mentioning non-blocking issue is MESON#3670.