unwinder: ppc and ppc64

Signed-off-by: Jan Kratochvil <jan.kratochvil@redhat.com>
diff --git a/libdwfl/linux-pid-attach.c b/libdwfl/linux-pid-attach.c
index e4eb621..45a0732 100644
--- a/libdwfl/linux-pid-attach.c
+++ b/libdwfl/linux-pid-attach.c
@@ -205,6 +205,14 @@
 			       const Dwarf_Word *regs, void *arg)
 {
   Dwfl_Thread *thread = (Dwfl_Thread *) arg;
+  if (firstreg < 0)
+    {
+      assert (firstreg == -1);
+      assert (nregs == 1);
+      INTUSE(dwfl_thread_state_register_pc) (thread, *regs);
+      return true;
+    }
+  assert (nregs > 0);
   return INTUSE(dwfl_thread_state_registers) (thread, firstreg, nregs, regs);
 }