xerces-c: New version 3.1.2
xerces-c: New version 3.1.2

Import xerces-c from upstream linuxbrew/homebrew. Use latest version
rather than older 3.1.1 from Cadfael 1.1.1 as the patch version
includes significant bug fixes and should not affect client packages.

xgarrido/homebrew-cadfael,SuperNEMO-DBD/homebrew-cadfael,SuperNEMO-DBD/homebrew-cadfael,xgarrido/homebrew-cadfael