amd64: added clobber for r8 to syscall5 to keep GCC from assuming r8 is valid.
amd64: added clobber for r8 to syscall5 to keep GCC from assuming r8 is valid.

jmolloy/pedigree,jmolloy/pedigree,jmolloy/pedigree,jmolloy/pedigree,jmolloy/pedigree,jmolloy/pedigree,jmolloy/pedigree