Add interruptor utilities

Expose wrapper functions for interrupting blocking calls, for process
and sockets.

app/src/util/process_intr.c

@@ -0,0 +1,16 @@
+#include "process_intr.h"
+
+bool
+sc_process_check_success_intr(struct sc_intr *intr, sc_pid pid,
+                              const char *name) {
+    if (!sc_intr_set_process(intr, pid)) {
+        // Already interrupted
+        return false;
+    }
+
+    // Always pass close=false, interrupting would be racy otherwise
+    bool ret = sc_process_check_success(pid, name, false);
+
+    sc_intr_set_process(intr, SC_PROCESS_NONE);
+    return ret;
+}