patch 8.1.0314: build failure without the +eval feature

Problem:    Build failure without the +eval feature. (Brenton Horne)
Solution:   Add #ifdef.  Also add the "dirty" item.
diff --git a/src/testdir/test_swap.vim b/src/testdir/test_swap.vim
index b0e2ec9..c12693c 100644
--- a/src/testdir/test_swap.vim
+++ b/src/testdir/test_swap.vim
@@ -109,6 +109,7 @@
   call assert_match('\w', info.user)
   call assert_equal(hostname(), info.host)
   call assert_match('Xswapinfo', info.fname)
+  call assert_match(0, info.dirty)
   call assert_equal(getpid(), info.pid)
   call assert_match('^\d*$', info.mtime)
   if has_key(info, 'inode')
@@ -128,6 +129,6 @@
 
   call writefile([repeat('x', 10000)], 'Xnotaswapfile')
   let info = swapinfo('Xnotaswapfile')
-  call assert_equal('magic number mismatch', info.error)
+  call assert_equal('Not a swap file', info.error)
   call delete('Xnotaswapfile')
 endfunc