stdenvNoCC should not inject any C++ standard library, just as it
doesn't inject any C standard library. stdenv still does, but only
indirectly through stdenv.cc. Wrapped clangs can be simplified now that
they don't need to worry about clobbering CoreFoundation when replacing
the C++ standard library implementation.
This generally-good cleanup should assist with debugging some C++
failures in #26805.
The source distribution contains binaries (probably for testing) that
make the Avira virus scanner treat it as malware on account of a “bad
ELF header”. Apart from being preferable in general, the HTTPS download
makes the file opaque to the overeager AV scanner in transparent
proxying setups.
Also adapt to the fact that the canonical downloads now point to a URL
like this:
https://releases.llvm.org/4.0.1/llvm-4.0.1.src.tar.xz
Needed to build an executable that uses OpenMP with clang. This
includes a header file and a library that clang will link into an
executable whose source makes use of ‘omp‘ pragmas.
This reflects upstream versioning change, and allows
us to replace 4.0 with 4.1 (which is now a minor revision)
without changing the attribute name.
Thanks to @vcunat for the idea.
