How to setup vim to edit both Makefile and normal code files?

This is a section of my .vimrc:

" enable filetype detection:
filetype on
filetype plugin on
filetype indent on " file type based indentation

" recognize anything in my .Postponed directory as a news article, and anything
" at all with a .txt extension as being human-language text [this clobbers the
" `help' filetype, but that doesn't seem to prevent help from working
" properly]:
augroup filetype
  autocmd BufNewFile,BufRead */.Postponed/* set filetype=mail
  autocmd BufNewFile,BufRead *.txt set filetype=human
augroup END

autocmd FileType mail set formatoptions+=t textwidth=72 " enable wrapping in mail
autocmd FileType human set formatoptions-=t textwidth=0 " disable wrapping in txt

" for C-like  programming where comments have explicit end
" characters, if starting a new line in the middle of a comment automatically
" insert the comment leader characters:
autocmd FileType c,cpp,java set formatoptions+=ro
autocmd FileType c set omnifunc=ccomplete#Complete

" fixed indentation should be OK for XML and CSS. People have fast internet
" anyway. Indentation set to 2.
autocmd FileType html,xhtml,css,xml,xslt set shiftwidth=2 softtabstop=2

" two space indentation for some files
autocmd FileType vim,lua,nginx set shiftwidth=2 softtabstop=2

" for CSS, also have things in braces indented:
autocmd FileType css set omnifunc=csscomplete#CompleteCSS

" add completion for xHTML
autocmd FileType xhtml,html set omnifunc=htmlcomplete#CompleteTags

" add completion for XML
autocmd FileType xml set omnifunc=xmlcomplete#CompleteTags

" in makefiles, don't expand tabs to spaces, since actual tab characters are
" needed, and have indentation at 8 chars to be sure that all indents are tabs
" (despite the mappings later):
autocmd FileType make set noexpandtab shiftwidth=8 softtabstop=0

" ensure normal tabs in assembly files
" and set to NASM syntax highlighting
autocmd FileType asm set noexpandtab shiftwidth=8 softtabstop=0 syntax=nasm

The section should be self-explanatory, but I suggest you read the vim help on filetype and autocmd.

The most relevant line to you, is probably this one:

autocmd FileType make set noexpandtab shiftwidth=8 softtabstop=0

make sure filetype detection is switched on, though.

Instead of doing this with autocmds, you could create your own user filetype plugin for each filetype, and place it in ~/.vim/ftplugin/<filetype>.vim, where <filetype> is the actual file type you want. For example:

mkdir -p ~/.vim/ftplugin
echo "setlocal noexpandtab" > ~/.vim/ftplugin/make.vim

You do need to make sure you have filetype plugins enabled in your ~/.vimrc with the following command:

filetype plugin on