The second release candidates for the 1.72.0 release are now available at:

<https://dl.bintray.com/boostorg/release/1.72.0/source/>

I have built this with the following configurations:
    Mac OS 10.11.6 with Apple LLVM version 8.0.0 (clang-800.0.42.1)
    Successful build with C++03/11/14/17

    Mac OS 10.11.6 with with clang trunk:
    Successful build with C++03/11/14/
    Unsuccessful build of Boost.Log with C++17/2a
        Note that this is a libc++ issue, not a Boost or Boost.Log issue.