systemc: Improve handling of empty process handles.

Most had checks, but didn't print any message. throw_it needed a check
as well.

Change-Id: I916c837112f9b27852583f01b3e16a6f53d5e7ca
Reviewed-on: https://gem5-review.googlesource.com/c/12440
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

src/systemc/ext/core/sc_process_handle.hh

@@ -33,7 +33,8 @@
 #include <exception>
 #include <vector>
 
-#include "systemc/ext/core/sc_object.hh"
+#include "../utils/sc_report_handler.hh"
+#include "sc_object.hh"
 
 namespace sc_gem5
 {
@@ -212,6 +213,11 @@ class sc_process_handle
              sc_descendent_inclusion_info include_descendants=
              SC_NO_DESCENDANTS)
     {
+        if (!_gem5_process) {
+            SC_REPORT_WARNING("(W570) attempt to use an empty "
+                    "process handle ignored", "throw_it()");
+            return;
+        }
         ::sc_gem5::ExceptionWrapper<T> exc(user_defined_exception);
         ::sc_gem5::throw_it_wrapper(_gem5_process, exc,
                 include_descendants == SC_INCLUDE_DESCENDANTS);

src/systemc/ext/utils/sc_report.hh

@@ -33,7 +33,7 @@
 #include <exception>
 #include <string>
 
-#include "systemc/ext/core/sc_time.hh"
+#include "../core/sc_time.hh"
 
 namespace sc_core
 {