This header doesn't exists on FreeBSD. According to https://www.gnu.org/software/gnulib/manual/html_node/error_002eh.html the function that this header implements are not present in the file. So there isn't any need for this header.
Created attachment 220879 [details] Remove unused error.h header
Comment on attachment 220879 [details] Remove unused error.h header set review flag
Fwiw i have the same issue on OpenBSD when trying to update our webkit from 2.2.4 to 2.3.5 - removing the inclusion of error.h fixes the build breakage.
Committed r164583: <http://trac.webkit.org/changeset/164583>