glibc 2.3.4 does not appear to define PTRACE_GETSIGINFO. This was
observed on a RHEL5 system on s390. Provide a suitable definition.
Tweak gdbserver_tests/filter_stderr to ignore messages related to
interrupted poll system calls.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14197 a5019735-40e9-0310-863c-91ae7b9d1cf9