crossfiles: Streamline and simplify crossfiles

• needs_exe_wrapper is only needed in specific cases when exe_wrapper is not set. See https://mesonbuild.com/Cross-compilation.html#properties

• "Before 0.56.0, _args and _link_args must be put in the properties section instead, else they will be ignored." [https://mesonbuild.com/Machine-files.html#meson-builtin-options] Our minimum version is 0.49.0. Meson >= 0.56.0 prints a deprecation warning.