b1782ee3d6
Building the C++ unit tests failed for
tests/src/App/Metadata.cpp
tests/src/Base/Reader.cpp
because some XML headers were not found. This was because the XercesC
include dir was not in the search list for headers.
I cannot say why only macOS seems to be affected, but it's not the first
time, see e.g a1776d3e74