Remove some of the support for obsolete IRIX 4 and 5

[Bruno Haible]

We don't need to support IRIX 4 and 5 any more, since IRIX 6 was released
in 1994 [1]. This patch removes some of the support for these systems,
where it is clear that it has no impact on IRIX 6. Namely, IRIX 5.3 and 6.5
have getmntent() in libc.

[1] https://en.wikipedia.org/wiki/IRIX#History


2020-12-20  Bruno Haible  <bruno@clisp.org>

        Remove some of the support for obsolete IRIX 4 and 5.
        * m4/mountlist.m4 (AC_FUNC_GETMNTENT): Don't test for getmntent in
        libsun.
        * tests/init.sh (setup_): Don't talk about IRIX 5.

diff --git a/m4/mountlist.m4 b/m4/mountlist.m4
index 7756955..ec49036 100644
--- a/m4/mountlist.m4
+++ b/m4/mountlist.m4
@@ -1,4 +1,4 @@
-# serial 14
+# serial 15
 dnl Copyright (C) 2002-2006, 2009-2020 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -331,8 +331,8 @@ AC_DEFUN([gl_PREREQ_MOUNTLIST_EXTRA],
 # nowadays.
 AC_DEFUN([AC_FUNC_GETMNTENT],
 [
-  # getmntent is in the standard C library on UNICOS, in -lsun on Irix 4,
-  # -lgen on Unixware.
-  AC_SEARCH_LIBS([getmntent], [sun gen])
+  # getmntent is in the standard C library on most systems, but in -lgen on
+  # Unixware.
+  AC_SEARCH_LIBS([getmntent], [gen])
   AC_CHECK_FUNCS([getmntent])
 ])
diff --git a/tests/init.sh b/tests/init.sh
index b4a5944..8938a1f 100644
--- a/tests/init.sh
+++ b/tests/init.sh
@@ -389,7 +389,7 @@ setup_ ()
   if test "$VERBOSE" = yes; then
     # Test whether set -x may cause the selected shell to corrupt an
     # application's stderr.  Many do, including zsh-4.3.10 and the /bin/sh
-    # from SunOS 5.11, OpenBSD 4.7 and Irix 5.x and 6.5.
+    # from SunOS 5.11, OpenBSD 4.7 and Irix 6.5.
     # If enabling verbose output this way would cause trouble, simply
     # issue a warning and refrain.
     if $gl_set_x_corrupts_stderr_; then