heapify: Include <stdlib.h> un generated C code

It is required for declarations of the malloc and free functions,
otherwise future compilers will not be able to build the generated
code because they do not support implicit function declarations by
default.

This also addresses potential crashes on 64-bit architectures if
the 64-bit pointer returned by malloc is truncated to 32 bits
because of the int return type of the implicit malloc declaration.

src/ext/heapify/heapify.ml

@@ -148,6 +148,7 @@ let default_heapify (f : file) =
   let free_fun = emptyFunction "free" in
   let alloc_exp = (Lval((Var(alloc_fun.svar)),NoOffset)) in
   let free_exp = (Lval((Var(free_fun.svar)),NoOffset)) in
+  f.globals <- GText("#include <stdlib.h>\n") :: f.globals ;
   ignore (heapify f alloc_exp free_exp)
 
 (* StackGuard clone *)
@@ -195,7 +196,9 @@ let default_stackguard (f : file) =
   let get_ra = expify (emptyFunction "stackguard_get_ra") in
   let set_ra = expify (emptyFunction "stackguard_set_ra") in
   let global_decl = 
-"extern void * stackguard_get_ra();
+"#include <stdlib.h>
+
+extern void * stackguard_get_ra();
 extern void stackguard_set_ra(void *new_ra);
 /* You must provide an implementation for functions that get and set the
  * return address. Such code is unfortunately architecture specific.