Define "exception classes" w/--disable-exceptions

We can still query these for what() even we can't throw them.

At least with gcc, -fno-exceptions still has the same policy with
std::exception etc., so we can still use those as superclasses.

Author: roystgnr

include/base/libmesh_exceptions.h

@@ -22,13 +22,10 @@
 
 #include "libmesh/libmesh_config.h"
 
-#ifdef LIBMESH_ENABLE_EXCEPTIONS
 #include <stdexcept>
 #include <string>
 #include <sstream>
 
-#define libmesh_noexcept noexcept
-
 namespace libMesh {
 
 /**
@@ -145,6 +142,9 @@ class SolverException: public std::exception
 
 }
 
+#ifdef LIBMESH_ENABLE_EXCEPTIONS
+#define libmesh_noexcept noexcept
+
 #define LIBMESH_THROW(e) do { throw e; } while (0)
 #define libmesh_try try
 #define libmesh_catch(e) catch(e)