Update devel/libclc to latest snapshot

[rezny]

Summary

This is the latestest snapshot, the version that I had been using for early testing of Mesa 17 with LLVM 4.0, and the subject of PR 218195. In an effort to keep everything on one version of LLVM, I have made libclc follow MESA_LLVM_VER so setting that in make.conf will affect libclc and Mesa. This is currently only useful to ease testing of the graphics stack with future LLVM releases since there is no version of libclc that supports both llvm39 and llvm40. License block re-ordered to satisfy portlint.

Test Plan

Poudriere 10.3/11.0 amd64/i386 OK

[jmd]

Thanks, I like the change.

[rezny]

Update the BUILD_DEPENDS on llvm to make the requirement more explicit since lowering LLVMVER is not expected to work.

[swills]

Approved