Last nightly fails to build macosx-toolchain

This is the build log:

-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Performing Test LLVM_LIBSTDCXX_MIN
-- Performing Test LLVM_LIBSTDCXX_MIN - Failed
CMake Error at cmake/modules/CheckCompilerVersion.cmake:97 (message):
  libstdc++ version must be at least 5.1.
Call Stack (most recent call first):
  cmake/config-ix.cmake:14 (include)
  CMakeLists.txt:670 (include)


-- Configuring incomplete, errors occurred!
See also "/var/tmp/build/build_clang/CMakeFiles/CMakeOutput.log".
See also "/var/tmp/build/build_clang/CMakeFiles/CMakeError.log".

/cc @pierov

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information