pactest: fix --gdb option

A libtool upgrade broke the gdb option as we need a MODE specified; add the
execute mode to the call.

Signed-off-by: Dan McGee <dan@archlinux.org>

pactest/pmtest.py

@@ -197,7 +197,7 @@ class pmtest:
             cmd.append("fakechroot")
 
         if pacman["gdb"]:
-            cmd.append("libtool gdb --args")
+            cmd.append("libtool execute gdb --args")
         if pacman["valgrind"]:
             cmd.append("valgrind -q --tool=memcheck --leak-check=full --show-reachable=yes")
         cmd.append("\"%s\" --config=\"%s\" --root=\"%s\" --dbpath=\"%s\" --cachedir=\"%s\"" \