Make _dl_relocate_static_pie return an int indicating whether it applied relocs.

There are two versions of _dl_relocation_static_pie. One of them is the
actual worker used for static pie which applies the startup relocations.
The other is a dummy use for non-pie static. This change make the worker
version return 1, and the dummy version return 0. The return value 1
indicates that the relocs have been applied, and hence a second round of
irel relocations are not attempted in LIBC_START_MAIN for static-pie.