patch 9.1.1466: filetype: not all lex files are recognized

Problem:  filetype: not all lex files are recognized
Solution: detect *.ll as lex, llvm or lifelines filetype, depending on
          the content (Eisuke Kawashima)

closes: #17560

Signed-off-by: Eisuke Kawashima <e-kwsm@users.noreply.github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/testdir/test_filetype.vim

@@ -2634,6 +2634,12 @@ func Test_ll_file()
   call assert_equal('llvm', &filetype)
   bwipe!
 
+  " lex (C++)
+  call writefile(['%{', '#include <iostream>', '%}'], 'Xfile.ll', 'D')
+  split Xfile.ll
+  call assert_equal('lex', &filetype)
+  bwipe!
+
   " lifelines
   call writefile(['proc main() {}'], 'Xfile.ll', 'D')
   split Xfile.ll

src/version.c

@@ -709,6 +709,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1466,
 /**/
     1465,
 /**/