patch 8.2.3050: cannot recognize elixir files

Problem:    Cannot recognize elixir files.
Solution:   Recognize Elixir-specific files.  Check if an .ex file is Euphoria
            or Elixir. (Austin Gatlin, closes #8401, closes #8446)
diff --git a/runtime/autoload/dist/ft.vim b/runtime/autoload/dist/ft.vim
index 1ac74b5..ac80659 100644
--- a/runtime/autoload/dist/ft.vim
+++ b/runtime/autoload/dist/ft.vim
@@ -172,6 +172,17 @@
   setf dtd
 endfunc
 
+func dist#ft#ExCheck()
+  let lines = getline(1, min([line("$"), 100]))
+  if exists('g:filetype_euphoria')
+    exe 'setf ' . g:filetype_euphoria
+  elseif match(lines, '^--\|^ifdef\>\|^include\>') > -1
+    setf euphoria3
+  else
+    setf elixir
+  endif
+endfunc
+
 func dist#ft#EuphoriaCheck()
   if exists('g:filetype_euphoria')
     exe 'setf ' . g:filetype_euphoria