Fix compilation of gmlmip with newest ocaml

The CAMLparam0() macro must be invoked at the beginning of a function
that has local variables.

src/lib/gmlmip_stub.c

@@ -24,6 +24,7 @@ extern "C" {
 
 template<class T>
 value set2CamlList(const set<T>& vec, value (*f)(const T&)) {
+    CAMLparam0();
     CAMLlocal2( cli, cons );
     cli = Val_emptylist;
 
@@ -45,6 +46,7 @@ value set2CamlList(const set<T>& vec, value (*f)(const T&)) {
 
 
 static CAMLprim value pair2caml(const int& t) {
+    CAMLparam0();
     CAMLlocal1( abc );
     abc = caml_alloc(2, 0);
     bool neg = t < 0;