Exit: Reorder the cleanup code somewhat.

exit_mc() calls exit_interleave_mutex(), which in turn calls
{init,exit}_threads_disable(), both of which mess with the
Pike_compile_cond. As the Pike_compile_cond is destroyed by
cleanup_pike_compiler() (called by cleanup_program()), make
sure that exit_mc() is called prior to cleanup_program().

Fixes issues on exit on some architectures and build options.

Potential fix for [PIKE-78]/[LysLysKOM 22448381].