ci: Add jobs for building binaries for Windows and Linux

ci: Add jobs for building binaries for Windows and Linux

Build binaries for x86_64 and aarch64 on Linux, and i686, x86_64
and aarch64 for Windows.

The Windows binaries are cross compiled from Linux. For x86, it
uses distro provided compilers, while it uses llvm-mingw installed
separately for targeting aarch64. (Most distros don't have packages
for mingw cross compilers for targeting Windows on aarch64 yet. GCC
isn't mature for this target yet, but Clang has supported this
target for many years now. Llvm-mingw is essentially the same toolchain
setup as MSYS2 uses in their clangarm64 environment, but available
as a standalone cross compiler too.)