This is somewhat non-obvious since there is no way to override curl
configure's use of pkg-config for NSS... it needs actually 2 include
paths, and the --with-nss takes only one (which is extended with
include/ and lib/).

Thanks to Alex Thurgood for the report.

Change-Id: I06074de50daad19a2cc62fe4090d3c0fbfdb2cb1