FreeCAD 0.20 is out now and I'd like to propose a PKGBUILD for it, some of the changes:
•the upstream URL was updated.
•switched to a source tarball as this significantly reduces the download size compared to a git clone (70M vs 1.6G).
•possibly not needed patches removed, please check this as I don't know what those are supposed to fix but I didn't find any problem compiling and running without them.
•the dependencies were updated (added optdepends, removed some seemingly unnecessary, added new ones) based on the cmake an namcap outputs as well as freecad forum discussions, please review and comment on this in case there's valid reasons to have the removed packages there.
•improved cmake flags
-c++17 was adopted as minimum version during 0.20 development
-the BUILD_PLOT flag mentioned in another bug report is not necessary in 0.20 as it is on by default
-the BUILD_FLAT_MESH flag enables a useful feature to flatten meshes
-INSTALL_TO_SITEPACKAGES install a freecad module so freecad can be imported from python without messing around with paths
-explicitly specifying CMAKE_INSTALL_LIBDIR is necessary to make the above work correctly
-by setting CMAKE_INSTALL_DATAROOTDIR various now unnecessary packaging steps can be removed

Here you can find a package built in a clean chroot with this PKGBUILD: https://github.com/adrianinsaval/pacman-repo/releases/download/archlinux-x86_64/freecad-0.20-1-x86_64.pkg.tar