FreeBSD 10 was the first release that officially released with Clang as the default, base compiler.
Most ports, unless specially marked, now compile using the base ("pre-installed") clang.
However, clang development is moderately rapid, and so the version of clang in base can be out of date frequently - not only do we have to wait for clang to be imported into base, but then we have to recompile from base (
make world) to install it; the other alternative for the more enterprising operator would be to navigate the source tree and attempt to rebuild and reinstall just clang.
It would be a lot easier to just use the version of clang that's in ports under lang/clangXX. Installing that's easy enough, but then how does one modify the ports infrastructure to use that install of clang instead of the base install of clang?