fix decl of ruby_single_main_ractor
On windows, MJIT doesn't work without this patch because of the declaration of ruby_single_main_ractor. This patch fix this issue and move the definition of it from ractor.c to vm.c to locate near place of ruby_current_vm_ptr.
fix decl of ruby_single_main_ractor
On windows, MJIT doesn't work without this patch because of
the declaration of ruby_single_main_ractor. This patch fix this
issue and move the definition of it from ractor.c to vm.c to locate
near place of ruby_current_vm_ptr.