Support setting settings with g:ale_pattern_options

autoload/ale/pattern_options.vim

@@ -13,6 +13,10 @@ function! ale#pattern_options#SetOptions() abort
     endfor
 
     for l:key in keys(l:options)
+        if l:key[:0] ==# '&'
+            call setbufvar(bufnr(''), l:key, l:options[l:key])
+        else
             let b:[l:key] = l:options[l:key]
+        endif
     endfor
 endfunction

test/test_pattern_options.vader

@@ -1,5 +1,7 @@
 Before:
-  Save g:ale_pattern_options, g:ale_pattern_options_enabled
+  Save g:ale_pattern_options
+  Save g:ale_pattern_options_enabled
+  Save &filetype
 
 After:
   Restore
@@ -11,6 +13,7 @@ Execute(Buffer variables should be set when filename patterns match):
   let g:ale_pattern_options = {'baz.*\.js': {
   \ 'ale_enabled': 1,
   \ 'some_option': 347,
+  \ '&filetype': 'pattern_option_set_filetype',
   \}}
 
   silent! file foobar.js
@@ -26,3 +29,4 @@ Execute(Buffer variables should be set when filename patterns match):
 
   AssertEqual 1, b:ale_enabled
   AssertEqual 347, b:some_option
+  AssertEqual 'pattern_option_set_filetype', &filetype