The hashes for libc++ and libc++abi were wrong.
There was also an incompatibility with nixpkgs on darwin which is now
weakly worked around: the "os_trace" macro changed definition in the OS
X development SDK since version 10.9 as used by nixpkgs. LLVM 3.8 uses
the new version, which I am temporarily replacing with a printf on
darwin as it is only used in one minor location.
vcunat's review:
- let's not switch the default versions of llvm* for now
- the only changes I see is adding python to clang's buildInputs
and using the big so-file as discussed in #12759
(BUILD_SHARED_LIBS -> LLVM_LINK_LLVM_DYLIB)
- in future it will be nice to split libLLVM into a separate output