patch 9.1.0866: filetype: LLVM IR files are not recognized

Problem:  filetype: LLVM IR files are not recognized
Solution: detect '*.ll' files either as lifelines or llvm filetype
          (Wu, Zhenyu)

closes: #15824

Signed-off-by: Wu, Zhenyu <wuzhenyu@ustc.edu>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/autoload/dist/ft.vim

@@ -169,6 +169,14 @@ export def FTcls()
   endif
 enddef
 
+export def FTll()
+  if getline(1) =~ ';\|\<source_filename\>\|\<target\>'
+    setf llvm
+  else
+    setf lifelines
+  endif
+enddef
+
 export def FTlpc()
   if exists("g:lpc_syntax_for_c")
     var lnum = 1

runtime/filetype.vim

@@ -1351,7 +1351,7 @@ au BufNewFile,BufRead */etc/sensors.conf,*/etc/sensors3.conf	setf sensors
 au BufNewFile,BufRead lftp.conf,.lftprc,*lftp/rc	setf lftp
 
 " Lifelines (or Lex for C++!)
-au BufNewFile,BufRead *.ll			setf lifelines
+au BufNewFile,BufRead *.ll			call dist#ft#FTll()
 
 " Lilo: Linux loader
 au BufNewFile,BufRead lilo.conf			setf lilo

runtime/ftplugin/llvm.vim

@@ -0,0 +1,12 @@
+" Vim filetype plugin file
+" Language:	LLVM IR
+" Last Change:	2024 Oct 22
+" Maintainer:	Wu, Zhenyu <wuzhenyu@ustc.edu>
+
+if exists("b:did_ftplugin") | finish | endif
+let b:did_ftplugin = 1
+
+setl comments=:;
+setl commentstring=;\ %s
+
+let b:undo_ftplugin = "setl commentstring< comments<"