Include <mutex> for std::once.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@204632 91177308-0d34-0410-b5e6-96231b3b80d8
Add annotation for test failure due to clang 3.4

FreeBSD recently updated to Clang 3.4 and the TestFormatters test case
started failing as it omits the C1 complete object constructor when not
needed.

llvm.org/pr19011


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@204652 91177308-0d34-0410-b5e6-96231b3b80d8