patch 8.2.1410: adding compiler plugin requires test change

Problem:    Adding compiler plugin requires test change.
Solution:   Include compiler plugin and adjust test.

runtime/compiler/xo.vim

@@ -0,0 +1,26 @@
+" Vim compiler file
+" Compiler:	XO
+" Maintainer:	Doug Kearns <dougkearns@gmail.com>
+" Last Change:	2019 Jul 10
+
+if exists("current_compiler")
+  finish
+endif
+let current_compiler = "xo"
+
+if exists(":CompilerSet") != 2		" older Vim always used :setlocal
+  command -nargs=* CompilerSet setlocal <args>
+endif
+
+let s:cpo_save = &cpo
+set cpo&vim
+
+" CompilerSet makeprg=npx\ xo\ --reporter\ compact
+
+CompilerSet makeprg=xo\ --reporter\ compact
+CompilerSet errorformat=%f:\ line\ %l\\,\ col\ %c\\,\ %trror\ %m,
+		       \%f:\ line\ %l\\,\ col\ %c\\,\ %tarning\ %m,
+		       \%-G%.%#
+
+let &cpo = s:cpo_save
+unlet s:cpo_save