It’s needed for [bcc][1].

    Submodule path 'src/cc/libbpf': checked out 'd5b146fec50d7aa126fe98323aeaee688d4af289'
    -- Latest recognized Git tag is v0.8.0
    -- Git HEAD is 339587fa33b54fc12f4c0e46bf15b4e9a7434670
    -- Revision is 0.8.0-339587fa
    -- Performing Test HAVE_NO_PIE_FLAG
    -- Performing Test HAVE_NO_PIE_FLAG - Success
    -- Performing Test HAVE_REALLOCARRAY_SUPPORT
    -- Performing Test HAVE_REALLOCARRAY_SUPPORT - Success
    -- Found BISON: /usr/bin/bison (found version "3.0.4")
    -- Found FLEX: /usr/bin/flex (found version "2.6.0")
    -- Found LLVM: /usr/include 6.0.1
    -- Found LibElf: /usr/lib/libelf.so
    -- Performing Test ELF_GETSHDRSTRNDX
    -- Performing Test ELF_GETSHDRSTRNDX - Success
    CMake Error at /usr/lib/cmake/llvm/LLVM-Config.cmake:256 (message):
      Library 'bpfcodegen' is a direct reference to a target library for an
      omitted target.
    Call Stack (most recent call first):
      cmake/clang_libs.cmake:21 (llvm_map_components_to_libnames)
      src/cc/CMakeLists.txt:76 (include)

[1]: https://github.com/iovisor/bcc

Rebuild for LLVM 7.0.1 update, and while at it, update to the latest
release.

Remove unneeded patch.

The release notes are available on-line ([18.3.0][1], [18.3.3][2]).

[1]: https://www.mesa3d.org/relnotes/18.3.0.html
[2]: https://www.mesa3d.org/relnotes/18.3.3.html