Add support for kprintf via syslog() and MacOS os_log().

This seems moderately successful, I was able to get logging out of the
CLI build with syslog().  I may marely have been having trouble with
logging on my Mac.

kernel/log.c

@@ -3,9 +3,13 @@
 #include <stdarg.h>
 #include <string.h>
 #include <sys/uio.h>
+#include <syslog.h>
 #if LOG_HANDLER_NSLOG
 #include <CoreFoundation/CoreFoundation.h>
 #endif
+#if LOG_HANDLER_OS_LOG
+#include <os/log.h>
+#endif
 #include "kernel/calls.h"
 #include "util/sync.h"
 #include "util/fifo.h"
@@ -142,6 +146,14 @@ static void log_line(const char *line) {
     extern void NSLog(CFStringRef msg, ...);
     NSLog(CFSTR("%s"), line);
 }
+#elif LOG_HANDLER_SYSLOG
+static void log_line(const char *line) {
+    syslog(LOG_DEBUG, "%s", line);
+}
+#elif LOG_HANDLER_OS_LOG
+static void log_line(const char *line) {
+    os_log_fault(OS_LOG_DEFAULT, "%s", line);
+}
 #endif
 
 static void default_die_handler(const char *msg) {

xX_main_Xx.h

@@ -2,6 +2,7 @@
 #include <unistd.h>
 #include <signal.h>
 #include <errno.h>
+#include <syslog.h>
 #include "kernel/init.h"
 #include "kernel/fs.h"
 #include "fs/devices.h"
@@ -67,6 +68,8 @@ static inline int xX_main_Xx(int argc, char *const argv[], const char *envp) {
         }
     }
 
+    openlog(argv[0], 0, LOG_USER);
+
     char root_realpath[MAX_PATH + 1] = "/";
     if (root != NULL && realpath(root, root_realpath) == NULL) {
         perror(root);