This adds clang thread safety annotations to std::mutex and
std::lock_guard so code using these types can use these types directly
instead of having to wrap the types to provide annotations. These checks
when enabled by -Wthread-safety provide simple but useful static
checking to detect potential race conditions.
See http://clang.llvm.org/docs/ThreadSafetyAnalysis.html for details.
This patch was reviewed in http://reviews.llvm.org/D14731.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@263611 91177308-0d34-0410-b5e6-96231b3b80d8
