feat: cosmopolitan libc support

Added support for cosmopolitan libc.
Simply do `make COSMO=yes` and you'll get feuille.com, a working
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+ version bump.

util.c

@@ -15,11 +15,13 @@
 
 #include "util.h"
 
+#ifndef COSMOPOLITAN
 #include <stdarg.h>   /* for va_end, va_list, va_start                     */
 #include <stdio.h>    /* for snprintf, vsnprintf, vfprintf, BUFSIZ, stderr */
 #include <stdlib.h>   /* for exit                                          */
 #include <syslog.h>   /* for syslog, LOG_DEBUG, LOG_ERR                    */
 #include <unistd.h>   /* for getpid                                        */
+#endif
 
 #include "feuille.h"  /* for Settings, settings                            */