bug#33900: GNUmakefile mode colors fooled by colons in shell commands

[積丹尼 Dan Jacobson]

$ cat Makefile
U=https://www.example.com//forum.php?mod=forumdisplay
all:new
        if ! test -f old; then touch old; fi
        diff old new > $T || :
        if test -s $T; then cat $T; echo https://www.example.com/; fi
        mv new old
$ emacs -q Makefile
See the weird colors caused by colons etc. on these lines?

     1  U=https://www.example.com//forum.php?mod=forumdisplay
     4          diff old new > $T || :
     5          if test -s $T; then cat $T; echo https://www.example.com/; fi

emacs-version "26.1"