When started as "vi", run in vi-compatibility mode, and don't source
defaults.vim.  This can be submitted upstream.

--- vim-9.1.1700/runtime/defaults.vim.orig
+++ vim-9.1.1700/runtime/defaults.vim
@@ -14,6 +14,12 @@
   finish
 endif
 
+" When started as "vi", operate in compatible mode (unless you have a
+" .vimrc).
+if v:progname ==? "vi"
+  finish
+endif
+
 " Bail out if something that ran earlier, e.g. a system wide vimrc, does not
 " want Vim to use these default values.
 if exists('skip_defaults_vim')