thread_support: split out {,non-}recursive mutex

Split out the recursive and non-recursive mutex.  This split is needed
for platforms which may use differing types for the two mutex (e.g.
Win32 threads).

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@291145 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed