Add clang 9 and 10 compilers to pkg

[zoujiaqing]

It's strange why the clang compiler is deeply coupled to FreeBSD's kernel code. You want to use the PKG command to install other versions of the clang compiler.

pkg install clang9

pkg install clang10

 

[kpedersen]

Clang is provided by the llvm# packages.

# pkg install llvm9

I.e https://svnweb.freebsd.org/ports/head/devel/llvm60/

We have many versions available to us. Many more than most other operating systems and distros.