[Runtime] Move init_nomp.c to flangrti

[PeixinQiao]

The functions in init_nomp.c was added in libompstub.so. The ompstub linking "-lompstub" is planed to be removed in the driver. However, it is unknown how the functions in init_nomp.c are used. For example, as the description in ilmtp.n, "_mp_lcpu2" is used for sections directive, but there is no such runtime function generated for a OpenMP sections program. To be safe, move init_nomp.c to flangrti.