Use a reference with exception types that use vtables

GCC 8 warns about this.

Author: tautschnig

src/java_bytecode/expr2java.h

@@ -84,7 +84,7 @@ std::string floating_point_to_java_string(float_type value)
     {
       return std::stod(decimal) == value;
     }
-    catch(std::out_of_range)
+    catch(std::out_of_range&)
     {
       return false;
     }