[vim] Recognize more FileCheck comments

[miyuki]

Summary

Currently vim syntax highlighting recognizes 'CHECK:' as a special
comment, but not CHECK-DAG, CHECK-NOT and other CHECKs. This patch
adds rules for these comments.

[rogfer01]

Can you coalesce them in a single regular expression, like /;\s*CHECK-(NEXT|NOT|DAG|SAME|LABEL): (not sure if this is the right syntax but I hope you got the idea.

[miyuki]

Coalesced into a single regular expression

[rogfer01]

LGTM now. Thanks!

utils/vim/syntax/llvm.vim

 syn match   llvmConstant /\<DW_VIRTUALITY_[a-z_]\+\>/
 syn match   llvmConstant /\<DIFlag[A-Za-z]\+\>/
 
 " Syntax-highlight lit test commands and bug numbers.
 syn match  llvmSpecialComment /;\s*PR\d*\s*$/
 syn match  llvmSpecialComment /;\s*REQUIRES:.*$/
 syn match  llvmSpecialComment /;\s*RUN:.*$/
 syn match  llvmSpecialComment /;\s*CHECK:.*$/
+syn match  llvmSpecialComment "\v;\s*CHECK-(NEXT|NOT|DAG|SAME|LABEL):.*$"
 syn match  llvmSpecialComment /;\s*XFAIL:.*$/
 
 if version >= 508 || !exists("did_c_syn_inits")
   if version < 508
     let did_c_syn_inits = 1
     command -nargs=+ HiLink hi link <args>
   else
     command -nargs=+ HiLink hi def link <args>