Bug 1317802 - don't stop for SIGSYS in .gdbinit; r=jld

The sandboxing code generates this signal nowadays, which makes
debugging with tools like rr quite frustrating.

DONTBUILD because NPOTB

.gdbinit

@@ -16,6 +16,7 @@ handle SIGPIPE noprint nostop pass
 # sandboxing code on older kernels.
 handle SIG38 noprint nostop pass
 handle SIG64 noprint nostop pass
+handle SIGSYS noprint nostop pass
 
 # Show the concrete types behind nsIFoo
 set print object on