clang-tidy: Ignore all of libclc source
clang-tidy: Ignore all of libclc source

libclc implements OpenCL C, which is not actual C/C++, and implements an
external API with different naming conventions.

As clang-tidy cannot parse the source[0], just blacklist all of libclc's
sources for now.

[0]: https://buildkite.com/llvm-project/premerge-checks/builds/695

google/llvm-premerge-checks,google/llvm-premerge-checks