Resize unamebuf[] to avoid warnings about snprintf() not having

enough buffer space.  Also change named_os_uname() prototype so
that it is now returning (const char *) rather than (char *).  If
uname() is not supported on a UNIX build prepopulate unamebuf[]
with "unknown architecture".

bin/named/unix/include/named/os.h

@@ -73,7 +73,7 @@ named_os_tzset(void);
 void
 named_os_started(void);
 
-char *
+const char *
 named_os_uname(void);
 
 #endif /* NAMED_OS_H */

bin/named/unix/os.c

@@ -903,8 +903,12 @@ named_os_tzset(void) {
 #endif /* ifdef HAVE_TZSET */
 }
 
-static char unamebuf[BUFSIZ];
-static char *unamep = NULL;
+#ifdef HAVE_UNAME
+static char unamebuf[sizeof(struct utsname)];
+#else
+static const char unamebuf[] = { "unknown architecture" };
+#endif
+static const char *unamep = NULL;
 
 static void
 getuname(void) {
@@ -919,13 +923,11 @@ getuname(void) {
 
 	snprintf(unamebuf, sizeof(unamebuf), "%s %s %s %s", uts.sysname,
 		 uts.machine, uts.release, uts.version);
-#else  /* ifdef HAVE_UNAME */
-	snprintf(unamebuf, sizeof(unamebuf), "unknown architecture");
 #endif /* ifdef HAVE_UNAME */
 	unamep = unamebuf;
 }
 
-char *
+const char *
 named_os_uname(void) {
 	if (unamep == NULL) {
 		getuname();

bin/named/win32/include/named/os.h

@@ -70,7 +70,7 @@ named_os_tzset(void);
 void
 named_os_started(void);
 
-char *
+const char *
 named_os_uname(void);
 
 #endif /* NAMED_OS_H */

bin/named/win32/os.c

@@ -393,7 +393,7 @@ named_os_started(void) {
 }
 
 static char unamebuf[BUFSIZ];
-static char *unamep = NULL;
+static const char *unamep = NULL;
 
 static void
 getuname(void) {
@@ -462,7 +462,7 @@ err:
  * GetVersionEx() returns 6.2 (aka Windows 8.1) since it was obsoleted
  * so we had to switch to the recommended way to get the Windows version.
  */
-char *
+const char *
 named_os_uname(void) {
 	if (unamep == NULL) {
 		getuname();