debugging v4 vcl -- check with "-C" fails, but give no error details

[grantksupport at operamail.com]

I'm plugging away at converting my v3 -> v4 vcl.

Made some progress, but right now, when I exec a config check it fails,
but provides no details,

 /usr/local/sbin/varnishd -C -n TEST -f
 /usr/local/etc/varnish/vcl.TEST.conf
  Running VCC-compiler failed, exit 1
  
  VCL compilation failed

How do I get some idea of what the problem is if the check isn't
reporting it?

Grant