Include type_traits in compare_types.h

We need this for std::enable_if

Author: roystgnr

include/utils/compare_types.h

@@ -19,15 +19,16 @@
 #ifndef LIBMESH_COMPARE_TYPES_H
 #define LIBMESH_COMPARE_TYPES_H
 
-// System includes
-#include <complex>
-
 #include "libmesh_config.h"
 
 #ifdef LIBMESH_DEFAULT_QUADRUPLE_PRECISION
 #include "libmesh_common.h" // for Real
 #endif
 
+// System includes
+#include <complex>
+#include <type_traits>
+
 namespace libMesh
 {