watch: define HOST_NAME_MAX

Those infernal arches of kfreebsd-i386 (not -amd64) don't define
HOST_NAME_MAX. This patch is a work-around for those systems with
lacking include files.

NEWS

@@ -1,3 +1,7 @@
+procps-ng-NEXT
+----------------
+  * watch: define HOST_NAME_MAX where not defined          Debian #830734
+
 procps-ng-3.3.12
 ----------------
   * libprocps API 6:0:0

watch.c

@@ -62,6 +62,10 @@
 # define isprint(x) ( (x>=' '&&x<='~') || (x>=0xa0) )
 #endif
 
+#ifndef HOST_NAME_MAX
+#define HOST_NAME_MAX 64
+#endif
+
 /* Boolean command line options */
 static int flags;
 #define WATCH_DIFF	(1 << 1)