Added the configuration command line and CFLAGS/CXXFLAGS to the snapshots and greeting message.

Does what it says on the tin. Just wanted to run it pass you in case you have a better way of doing this.

Thanks ! Branch can be removed.

src/riemann/riemann_exact.h

@@ -25,12 +25,18 @@
  *  Dynamics, Springer (2009, 3rd edition)
  *
  ******************************************************************************/
-
 #ifndef SWIFT_RIEMANN_EXACT_H
 #define SWIFT_RIEMANN_EXACT_H
 
+/* Some standard headers. */
 #include <float.h>
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+/* Local headers. */
 #include "adiabatic_index.h"
+#include "error.h"
 #include "minmax.h"
 #include "riemann_vacuum.h"