N3659: Shared locking in C++  Revision 2, c++1y only

llvm-svn: 191127
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: ead6f1699dcda74528393b328250cbcb47fb1211
39 files changed