/usr/include/gecode/support/ is in libgecode-dev 5.1.0-2build1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/gecode/support/allocator.hpp
/usr/include/gecode/support/auto-link.hpp
/usr/include/gecode/support/bitset-base.hpp
/usr/include/gecode/support/bitset-offset.hpp
/usr/include/gecode/support/bitset.hpp
/usr/include/gecode/support/block-allocator.hpp
/usr/include/gecode/support/cast.hpp
/usr/include/gecode/support/config.hpp
/usr/include/gecode/support/dynamic-array.hpp
/usr/include/gecode/support/dynamic-queue.hpp
/usr/include/gecode/support/dynamic-stack.hpp
/usr/include/gecode/support/exception.hpp
/usr/include/gecode/support/heap.hpp
/usr/include/gecode/support/hw-rnd.hpp
/usr/include/gecode/support/int-type.hpp
/usr/include/gecode/support/macros.hpp
/usr/include/gecode/support/marked-pointer.hpp
/usr/include/gecode/support/random.hpp
/usr/include/gecode/support/run-jobs.hpp
/usr/include/gecode/support/sort.hpp
/usr/include/gecode/support/static-stack.hpp
/usr/include/gecode/support/thread/
/usr/include/gecode/support/thread.hpp
/usr/include/gecode/support/thread/none.hpp
/usr/include/gecode/support/thread/pthreads.hpp
/usr/include/gecode/support/thread/thread.hpp
/usr/include/gecode/support/thread/windows.hpp
/usr/include/gecode/support/timer.hpp