Include signal.h, reorder headers

solaris/SolarisProcess.h

@@ -8,11 +8,15 @@ Released under the GNU GPLv2, see the COPYING file
 in the source distribution for its full text.
 */
 
-#include "Settings.h"
+#include "config.h" // IWYU pragma: keep
+
 #include <zone.h>
 #include <sys/proc.h>
 #include <libproc.h>
 
+#include "Settings.h"
+
+
 typedef struct SolarisProcess_ {
    Process    super;
    int        kernel;