runtime(syntax-tests): tiny vim fails because of line-continuation

Problem:  tiny vim fails because of line-continuation, although
          the test script should be skipped for non-eval builds of Vim.
Solution: :set cpo&vim

Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/syntax/testdir/runtest.vim

@@ -2,6 +2,9 @@
 "
 " Current directory must be runtime/syntax.
 
+" needed because of line-continuation lines
+set cpo&vim
+
 " Only do this with the +eval feature
 if 1