bug#55446: 29.0.50; Bad choice of indent-line-function in makefile-mode

[Po Lu]

A recent change in makefile-mode causes incorrect indentation of the
following text:

  FOO = @FOO@

Move to the end of @FOO@ and hit RET: the next line will be indented
with a tab, which is incorrect, and not how earlier versions of Emacs
behaved.

In GNU Emacs 29.0.50 (build 311, x86_64-pc-linux-gnu, GTK+ Version 3.24.31)
 of 2022-05-16 built on trinity
Repository revision: b8cfe8fa754e3a3d197b785a179e0915ba4f53bf
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12014000
System Description: Fedora Linux 35 (Workstation Edition)

Configured using:
 'configure --with-x-toolkit=gtk3 --without-cairo --with-dumping=unexec
 --cache-file=/tmp/ccache'

Configured features:
ACL DBUS FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG JSON LCMS2
LIBSELINUX LIBSYSTEMD LIBXML2 MODULES NOTIFY INOTIFY PNG RSVG SECCOMP
SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS UNEXEC WEBP X11 XDBE XFT
XIM XINPUT2 XPM GTK3 ZLIB

Important settings:
  value of $LANG: en_GB.UTF-8
  value of $XMODIFIERS: @im=none
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media rmc puny
dired dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg
rfc6068 epg-config gnus-util text-property-search time-date seq gv
subr-x byte-opt bytecomp byte-compile cconv mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader cl-loaddefs
cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
iso-transl tooltip eldoc paren electric uniquify ediff-hook vc-hooks
lisp-float-type elisp-mode mwheel term/x-win x-win term/common-win x-dnd
tool-bar dnd fontset image regexp-opt fringe tabulated-list replace
newcomment text-mode lisp-mode prog-mode register page tab-bar menu-bar
rfn-eshadow isearch easymenu timer select scroll-bar mouse jit-lock
font-lock syntax font-core term/tty-colors frame minibuffer nadvice
simple cl-generic cham georgian utf-8-lang misc-lang vietnamese tibetan
thai tai-viet lao korean japanese eucjp-ms cp51932 hebrew greek romanian
slovak czech european ethiopic indian cyrillic chinese composite
emoji-zwj charscript charprop case-table epa-hook jka-cmpr-hook help
abbrev obarray oclosure cl-preloaded button loaddefs faces cus-face
macroexp files window text-properties overlay sha1 md5 base64 format env
code-pages mule custom widget keymap hashtable-print-readable backquote
threads dbusbind inotify lcms2 dynamic-setting system-font-setting
font-render-setting move-toolbar gtk x-toolkit xinput2 x multi-tty
make-network-process emacs)

Memory information:
((conses 16 106194 6740)
 (symbols 48 21179 1)
 (strings 32 33393 1544)
 (string-bytes 1 910029)
 (vectors 16 16969)
 (vector-slots 8 560139 12198)
 (floats 8 55 72)
 (intervals 56 234 0)
 (buffers 992 10))