patch 9.0.0287: Irix systems no longer exist

Problem:    Irix systems no longer exist.
Solution:   Remove references to Irix. (Yegappan Lakshmanan, closes #10994)
diff --git a/src/install-sh b/src/install-sh
index 0b0fdcb..14d0b78 100644
--- a/src/install-sh
+++ b/src/install-sh
@@ -332,7 +332,7 @@
             then
               if test -z "$dir_arg" || {
                    # Check for POSIX incompatibilities with -m.
-                   # HP-UX 11.23 and IRIX 6.5 mkdir -m -p sets group- or
+                   # HP-UX 11.23 mkdir -m -p sets group- or
                    # other-writable bit of parent directory when it shouldn't.
                    # FreeBSD 6.1 mkdir -m -p sets mode of existing directory.
                    ls_ld_tmpdir=`ls -ld "$tmpdir"`