c6e466911f
Summary: In some places in libc++ we need to use the `__atomic_*` builtins. This patch adds a header that provides access to those builtins in a uniform way from within the dylib source. If the compiler building the dylib does not support these builtins then a warning is issued. Only relaxed loads are needed within the headers. A singe function to do these relaxed loads has been added to `<memory>`. This patch applies the new atomic builtins to `__shared_count` and `call_once`. Reviewers: mclow.lists Subscribers: majnemer, jroelofs, cfe-commits Differential Revision: http://reviews.llvm.org/D10406 git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@241532 91177308-0d34-0410-b5e6-96231b3b80d8