Don't allowing functions called from _Start to be inlined

When the partial inlining comes to the _Start function, it skips over
it. We don't want inlining on the start function because if we are
trying to find the entry point for the users code, it is important it
hasn't been inlined into GOTO generated code.

Author: thk123

src/goto-programs/goto_inline.cpp

@@ -213,7 +213,12 @@ void goto_partial_inline(
       // called function
       const goto_functiont &goto_function=f_it->second;
 
-      if(!goto_function.body_available())
+      // We can't take functions without bodies to find functions
+      // inside them to be inlined.
+      // We also don't allow for the _start function to have any of its
+      // function calls to be inlined
+      if(!goto_function.body_available() ||
+         f_it->first==ID__start)
         continue;
 
       const goto_programt &goto_program=goto_function.body;