patch 8.1.2358: tests fail on Cirrus CI for FreeBSD

Problem:    Tests fail on Cirrus CI for FreeBSD.
Solution:   Fix a test and skip some. (Christian Brabandt, closes #5281)
diff --git a/src/testdir/check.vim b/src/testdir/check.vim
index 6c3b1be..30c4158 100644
--- a/src/testdir/check.vim
+++ b/src/testdir/check.vim
@@ -64,6 +64,15 @@
   endif
 endfunc
 
+" Command to check for not running on a BSD system.
+" TODO: using this checks should not be needed
+command CheckNotBSD call CheckNotBSD()
+func CheckNotBSD()
+  if has('bsd')
+    throw 'Skipped: does not work on BSD'
+  endif
+endfunc
+
 " Command to check that making screendumps is supported.
 " Caller must source screendump.vim
 command CheckScreendump call CheckScreendump()