patch 8.2.3584: "verbose set efm" reports location of the :compiler command

Problem:    "verbose set efm" reports the location of the :compiler command.
            (Gary Johnson)
Solution:   Add the "-keepscript" argument to :command and use it when
            defining CompilerSet.
diff --git a/src/testdir/test_compiler.vim b/src/testdir/test_compiler.vim
index ede307f..09c03f7 100644
--- a/src/testdir/test_compiler.vim
+++ b/src/testdir/test_compiler.vim
@@ -21,6 +21,9 @@
   call assert_equal('perl', b:current_compiler)
   call assert_fails('let g:current_compiler', 'E121:')
 
+  let verbose_efm = execute('verbose set efm')
+  call assert_match('Last set from .*/compiler/perl.vim ', verbose_efm)
+
   call setline(1, ['#!/usr/bin/perl -w', 'use strict;', 'my $foo=1'])
   w!
   call feedkeys(":make\<CR>\<CR>", 'tx')