No joy. I built a fresh Julia 0.7.0 from source, including all the dependencies. I then get:
(v0.7) pkg> add Cxx#master
Updating git-repo `https://github.com/Keno/Cxx.jl.git`
┌ Warning: project file for Cxx at /tmp/tmp9P4aqW is missing a version entry
└ @ Pkg.Types ~/Code/julia-0.7.0/usr/share/julia/stdlib/v0.7/Pkg/src/Types.jl:700
Resolving package versions…
Updating ~/.julia/environments/v0.7/Project.toml
[a0b5b9ef] + Cxx v0.2.0+ #master (GitHub - JuliaInterop/Cxx.jl: The Julia C++ Interface)
Updating ~/.julia/environments/v0.7/Manifest.toml
[a0b5b9ef] + Cxx v0.2.0+ #master (GitHub - JuliaInterop/Cxx.jl: The Julia C++ Interface)
Building Cxx → ~/.julia/packages/Cxx/81BGP/deps/build.log
┌ Error: Error building Cxx:
│ WARNING: JULIA_HOME environment variable is renamed to JULIA_BINDIR
│ mkdir src
│ curl -Lo src/cfe-6.0.0.src.tar.xz http://releases.llvm.org/6.0.0/cfe-6.0.0.src.tar.xz
│ Not building debug library because corresponding julia DEBUG library does not exist.
│ To build, simply run the build again once the library at
│ /libjulia-debug.so
│ has been built.
│ % Total % Received % Xferd Average Speed Time Time Time Current
│ Dload Upload Total Spent Left Speed
100 5307 0 5307 0 0 80409 0 --:–:-- --:–:-- --:–:-- 80409
│ mkdir -p src/clang-6.0.0
│ tar -C src/clang-6.0.0 --strip-components=1 -xf src/cfe-6.0.0.src.tar.xz
│ xz: (stdin): File format not recognized
│ tar: Child returned status 1
│ tar: Error is not recoverable: exiting now
│ BuildBootstrap.Makefile:103: recipe for target ‘src/clang-6.0.0’ failed
│ make: *** [src/clang-6.0.0] Error 2
│ [ Info: Building julia source build
│ ERROR: LoadError: failed process: Process(make -j12 -f BuildBootstrap.Makefile BASE_JULIA_BIN=/home/glen/Code/julia-0.7.0/usr/bin BASE_JULIA_SRC=/home/glen/Code/julia-0.7.0/usr/bin/../.., ProcessExited(2)) [2]
│ Stacktrace:
│ [1] error(::String, ::Base.Process, ::String, ::Int64, ::String) at ./error.jl:42
│ [2] pipeline_error at ./process.jl:712 [inlined]
│ [3] #run#509(::Bool, ::Function, ::Cmd) at ./process.jl:670
│ [4] run(::Cmd) at ./process.jl:668
│ [5] top-level scope at none:0
│ [6] include at ./boot.jl:317 [inlined]
│ [7] include_relative(::Module, ::String) at ./loading.jl:1038
│ [8] include(::Module, ::String) at ./sysimg.jl:29
│ [9] include(::String) at ./client.jl:398
│ [10] top-level scope at none:0
│ in expression starting at /home/glen/.julia/packages/Cxx/81BGP/deps/build.jl:54
│ writing path.jl file
│ Tuning for julia installation at /home/glen/Code/julia-0.7.0/usr/bin with sources possibly at /home/glen/Code/julia-0.7.0/usr/bin/…/…
└ @ Pkg.Operations ~/Code/julia-0.7.0/usr/share/julia/stdlib/v0.7/Pkg/src/Operations.jl:1068