This has the benefit of not requiring a 'runtime' IR file, so that
complete relocatable files can be built without requiring input IR.
This makes the compiler a lot easier to use without the Makefile.
Code size is not affected.
CGo depends on syscall, which (in the standard library) depends on sync,
which depends on the runtime. There are also other import cycles. To be
able to use the syscall package from upstream, stop using CGo.
