Would several separate runtime builds with each time one project in LLVM_ENABLE_RUNTIMES work, to replace standalone builds ?

In D81190#2896925, @ldionne wrote:

Does this commit not work on your system? It has been working on our Linux bots since it was committed.

I don't remember if I found a case which needed the library.
My question was more : on which system does linking libc++ with libatomic help ?

On which platform does this commit work ?

In D28791#668496, @phosek wrote:

We discussed this with @mcgrathr and came up with a possible alternative solution: Currently the only bit of crtbegin.o we're missing is the __dso_handle symbol because Clang generates a reference to it when compiling C++ code.

So only Fuchsia would be supported, Linux would still need external ctrbegin.o/crtend.o (from gcc by default, but for projects like https://blogs.gentoo.org/gsoc2016-native-clang/ there still won't be any good solution).