[vim] Add the IR's comment prefix to the comments list. This allows vim

to intelligently wrap prose written in IR comment blocks. This has
bothered me for roughly ever, and my fellow IRC denziens convinced me to
fix it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@242266 91177308-0d34-0410-b5e6-96231b3b80d8

utils/vim/ftplugin/llvm.vim

@@ -9,3 +9,4 @@ let b:did_ftplugin = 1
 
 setlocal softtabstop=2 shiftwidth=2
 setlocal expandtab
+setlocal comments+=:;