subversion: apply libtool patch for linking on 10.10

The subversion formula uses stdenv due to the serf -> scons dependency,
and since stdenv sets MACOSX_DEPLOYMENT_TARGET, we need to patch
configure to work around a bug in libtool (which is already fixed in
libtool upstream).

See commit a5a36f44ca6fb626929c13154b10d13380d78cf4, and
https://trac.macports.org/ticket/44596#comment:35 for more information.

Fixes #34644.