suppress more leaks in external libraries

Change-Id: Ia69ce6a7be9f995dc919b91e4a3a56375e1c4c96
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/115908
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

leak-suppress.txt

@@ -66,3 +66,10 @@ leak:Firebird::
 # these appears to be some kind of ref-counting cycle
 leak:SbiRuntime::
 leak:SbModule::
+
+# LibXML leaks a couple of objects
+leak:libxml2.so
+
+# LibCoin leaks a little
+leak:coinComputeIntVariables
+leak:CoinMessages::operator=(CoinMessages const&)