Enable sys_rt_sigsuspend on ppc64-linux.  Not sure why this is
necessary, but I found it lying around in a ppc64 tree, so there
was probably some use case at some point.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13668 a5019735-40e9-0310-863c-91ae7b9d1cf9