Slice-global-inits requires function-pointer removal

It uses `call_grapht`, which in turn expects function pointers to have
been resolved beforehand.

Author: tautschnig

regression/goto-instrument/slice-global-inits6/main.c

@@ -0,0 +1,9 @@
+int foo()
+{
+}
+
+int main()
+{
+  int (*fp)() = &foo;
+  (*fp)();
+}

regression/goto-instrument/slice-global-inits6/test.desc

@@ -0,0 +1,8 @@
+CORE
+main.c
+--slice-global-inits
+^VERIFICATION SUCCESSFUL$
+^EXIT=0$
+^SIGNAL=0$
+--
+^warning: ignoring

src/goto-instrument/goto_instrument_parse_options.cpp

@@ -1481,6 +1481,8 @@ void goto_instrument_parse_optionst::instrument_goto_program()
 
   if(cmdline.isset("slice-global-inits"))
   {
+    do_indirect_call_and_rtti_removal();
+
     log.status() << "Slicing away initializations of unused global variables"
                  << messaget::eom;
     slice_global_inits(goto_model, ui_message_handler);