Initial structure for supervisor-mode

The full process hierarchy isn't set up yet, but these changes
help prepare by doing two things:

- Add a -j option to enable supervisor-mode.  Currently, just a single
  "stem" process gets forked early on to be used as the basis for
  further forking into real cluster nodes.

- Separates the parsing of command-line options from their consumption.
  i.e. need to parse whether we're in -j supervisor-mode before
  modifying any global state since that would taint the "stem" process.
  The new intermediate structure containing the parsed options may
  also serve as a way to pass configuration info from "stem" to its
  descendent cluster node processes.

src/util.h

@@ -60,6 +60,15 @@ extern HeapLeakChecker* heap_checker;
 #endif
 
 #include <stdint.h>
+#include <pthread.h>
+
+#ifdef HAVE_LINUX
+#include <sys/prctl.h>
+#endif
+
+#ifdef __FreeBSD__
+#include <pthread_np.h>
+#endif
 
 ZEEK_DEPRECATED("Remove in v4.1. Use uint64_t instead.")
 typedef uint64_t uint64;
@@ -579,3 +588,14 @@ std::unique_ptr<T> build_unique (Args&&... args) {
  * @return the escaped string
  */
 std::string json_escape_utf8(const std::string& val);
+
+namespace zeek {
+/**
+ * Set the process/thread name.  May not be supported on all OSs.
+ * @param name  new name for the process/thread.  OS limitations typically
+ * truncate the name to 15 bytes maximum.
+ * @param tid  handle of thread whose name shall change
+ */
+void set_thread_name(const char* name, pthread_t tid = pthread_self());
+
+} // namespace zeek