FreeBSD support is incomplete

[assistcontrol]

I maintain the lua_ls port in FreeBSD, and I have to do some patching every time luamake is updated. It'd be nice if some of the changes were merged in here, rather than patching on every release.

• FreeBSD comes with clang and not gcc. Our packages are never built with gcc. I see that you have a clang spec; can freebsd.ninja be updated to use it instead of gcc?
• Compilation commands need -I/usr/loca/include, and linker commands need -L/usr/local/lib
• -Wno-maybe-uninitialized does not exist and causes clang to error out. Can it be -Wno-uninitialized instead?
• -Wl,-E causes clang to error, so we drop that word entirely

You can see FreeBSD's luamake patch here: https://github.com/freebsd/freebsd-ports/blob/main/devel/lua-language-server/files/patch-3rd_luamake_compile_ninja_freebsd.ninja

Thank you for all the work you've done to support FreeBSD!