add a comment; restore @ for more isalpha chars

Author: frasercrmck

llvm/utils/vim/ftplugin/llvm.vim

@@ -11,4 +11,11 @@ setlocal softtabstop=2 shiftwidth=2
 setlocal expandtab
 setlocal comments+=:;
 setlocal commentstring=;\ %s
-setlocal iskeyword=%,@-@,$,a-z,A-Z,48-57,_,.,-
+" We treat sequences of the following characters as forming 'keywords', with
+" the aim of easing movement around LLVM identifiers:
+" * identifier prefixes: '%' and '@' (@-@)
+" * all characters where isalpha() returns TRUE (@)
+" * the digits 0-9 (48-57)
+" * other characters that may form identifiers: '_', '.', '-', '$'
+" Comment this out to restore the default behaviour
+setlocal iskeyword=%,@-@,@,48-57,_,.,-,$