Add inline attribute.

* This way, gcc will not complain when size_t_c2f is unused.

src/cdiFortran.c

@@ -29,7 +29,7 @@
 #  pragma GCC diagnostic ignored "-Wmissing-prototypes"
 #endif
 
-static
+static inline
 int size_t_c2f(size_t value_size_t)
 {
   assert(value_size_t < INT_MAX);

src/cdipioFortran.c

@@ -29,7 +29,7 @@
 #  pragma GCC diagnostic ignored "-Wmissing-prototypes"
 #endif
 
-static
+static inline
 int size_t_c2f(size_t value_size_t)
 {
   assert(value_size_t < INT_MAX);

src/make_fint.c

@@ -438,7 +438,7 @@ static void fortran_interface(char *fname, char *fnameinc, char *fnameint,
         "#endif\n"
         "\n", fpint);
 
-  fputs("static\n"
+  fputs("static inline\n"
         "int size_t_c2f(size_t value_size_t)\n"
         "{\n"
         "  assert(value_size_t < INT_MAX);\n"