Use clang 6.0 in clang CI jobs
As our Docker images are now using clang 6.0, set CC
to clang-6.0
in our clang CI jobs as this is the name of the binary installed by Debian/Ubuntu clang 6.0 packages.
As our Docker images are now using clang 6.0, set CC
to clang-6.0
in our clang CI jobs as this is the name of the binary installed by Debian/Ubuntu clang 6.0 packages.