Import a proposed upstream bug fix to allow building against recent curl
versions. Fixes the following error observed by the buildbots:

    curlopt-constants.c:129:49: error: 'CURL_STRICTER' undeclared (first use in this function)
                 if (strEQ(name, "STRICTER")) return CURL_STRICTER;

Upstream bug: https://rt.cpan.org/Public/Bug/Display.html?id=117793

Signed-off-by: Jo-Philipp Wich <jo@mein.io>