Install the `kitty` command-line utility and the `kitty.app` macOS
application.
* Prefer libicns (png2icns) over Apple's non-free iconutil.
* Work around warnings from Apple headers by disabling -pedantic-errors
and -Werror.
* Work around ld not support LLVM-LTO by disabling LTO.
* Make Kitty and glfw compile for macOS 10.11 (and macOS 10.10).
