Use the "-fno-optimize-sibling-calls" gcc option to prevent GOT relocations
caused by gcc versions without the commit "S/390: Fix 64 bit sibcall":

 * https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=233169

Otherwise we get compile errors like:

 GEN      criu/pie/parasite-blob.h
 Error (compel/src/lib/handle-elf-host.c:572):
 Unsupported relocation of type 26

Those can be caused by the following relocation types:

 * R_390_GOTENT (e.g. RHEL7 based systems)
 * R_390_GOTPCDBL (e.g. Debian Jessie)
 * R_390_GOT12 (e.g. Debian Jessie)
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>