runtest.rb: use ninja.sh to handle export

[go] fix
 export_export.mk
 not_command_with_tab.mk
diff --git a/runtest.rb b/runtest.rb
index 0eb20ea..856846f 100755
--- a/runtest.rb
+++ b/runtest.rb
@@ -184,8 +184,8 @@
       end
       cmd += " #{tc} 2>&1"
       res = IO.popen(cmd, 'r:binary', &:read)
-      if via_ninja && File.exist?('build.ninja')
-        res += normalize_ninja_log(IO.popen('ninja -j1 -v', 'r:binary', &:read))
+      if via_ninja && File.exist?('build.ninja') && File.exists?('ninja.sh')
+        res += normalize_ninja_log(IO.popen('./ninja.sh -j1 -v', 'r:binary', &:read))
       end
       res = normalize_kati_log(res)
       output += "=== #{tc} ===\n" + res