www/webkit2-gtk3: fix build to allow eclipse to work - Disable PTHREAD_MAIN_NP PR: 238844 Submitted by: huanghwh@gmail.com, Jonathan Chen <jonc@chen.org.nz> Reported by: Patrick Mackinlay <freebsd.68fba@nospam.spacesurfer.com> Reviewed by: Michael Zhilin <mizhka@gmail.com>, misc-freebsd-bugzilla@talk2dom.com, Jose Quinteiro <freebsd@quinteiro.org>