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".

(cherry picked from commit 4bc3de070f)

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

@@ -73,7 +73,7 @@ ns_os_tzset(void);
 void
 ns_os_started(void);
 
-char *
+const char *
 ns_os_uname(void);
 
 #endif /* NS_OS_H */

bin/named/unix/os.c

@@ -1089,8 +1089,12 @@ ns_os_tzset(void) {
 #endif
 }
 
-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) {
@@ -1103,18 +1107,16 @@ getuname(void) {
 		return;
 	}
 
-	snprintf(unamebuf, sizeof(unamebuf),
-		 "%s %s %s %s",
-		 uts.sysname, uts.machine, uts.release, uts.version);
-#else
-	snprintf(unamebuf, sizeof(unamebuf), "unknown architecture");
-#endif
+	snprintf(unamebuf, sizeof(unamebuf), "%s %s %s %s", uts.sysname,
+		 uts.machine, uts.release, uts.version);
+#endif /* ifdef HAVE_UNAME */
 	unamep = unamebuf;
 }
 
-char *
+const char *
 ns_os_uname(void) {
-	if (unamep == NULL)
+	if (unamep == NULL) {
 		getuname();
+	}
 	return (unamep);
 }

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

@@ -70,7 +70,7 @@ ns_os_tzset(void);
 void
 ns_os_started(void);
 
-char *
+const char *
 ns_os_uname(void);
 
 #endif /* NS_OS_H */

bin/named/win32/os.c

@@ -392,7 +392,7 @@ ns_os_started(void) {
 }
 
 static char unamebuf[BUFSIZ];
-static char *unamep = NULL;
+static const char *unamep = NULL;
 
 static void
 getuname(void) {
@@ -461,9 +461,10 @@ getuname(void) {
  * 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 *
 ns_os_uname(void) {
-	if (unamep == NULL)
+	if (unamep == NULL) {
 		getuname();
+	}
 	return (unamep);
 }