Unbreak build with GCC >= 8

conftest.cpp:11:36: error: return-statement with a value, in function returning 'void' 

--- configure.orig	2018-10-30 17:53:07 UTC
+++ configure
@@ -17744,7 +17744,7 @@ if ac_fn_cxx_try_run "$LINENO"; then :
 #define ARGF f
 #endif
 template<typename ARG>
-  void detect_type(ARG)
+  int detect_type(ARG)
   {
     return reinterpret_cast<ARG*>(0);
   }