Declare a function with a prototype

From the C99 standard:
	An identifier list declares only the identifiers of the parameters of the function.
	An empty list in a function declarator that is part of a definition of that function
	specifies that the function has no parameters. The empty list in a function declarator
	that is not part of a definition of that function specifies that no information about
	the number or types of the parameters is supplied.

Because this is a function definition, not a simple delclaration, `void`
is not required. Yet, because the function has not declared beforehand,
I find it better to add `void`.

src/hdf5_dl.c

@@ -130,7 +130,7 @@ void *find_sym(void *handle, const char *symbol) {
  *
  * Returns: -1 if an error occured, 0 for success
  */
-int check_symbols() {
+int check_symbols(void) {
 
   if(DL_H5Functions.H5open == NULL)
     return -1;