remove use of Mutex in favour of std::{,recursive_}mutex

This is a pretty straightforward first pass over removing a number of uses of
Mutex in favor of std::mutex or std::recursive_mutex. The problem is that there
are interfaces which take Mutex::Locker & to lock internal locks. This patch
cleans up most of the easy cases. The only non-trivial change is in
CommandObjectTarget.cpp where a Mutex::Locker was split into two.

llvm-svn: 269877
diff --git a/lldb/source/Plugins/Process/FreeBSD/ProcessMonitor.cpp b/lldb/source/Plugins/Process/FreeBSD/ProcessMonitor.cpp
index 2318a65..16707a5 100644
--- a/lldb/source/Plugins/Process/FreeBSD/ProcessMonitor.cpp
+++ b/lldb/source/Plugins/Process/FreeBSD/ProcessMonitor.cpp
@@ -1348,7 +1348,7 @@
 void
 ProcessMonitor::DoOperation(Operation *op)
 {
-    Mutex::Locker lock(m_operation_mutex);
+    std::lock_guard<std::mutex> guard(m_operation_mutex);
 
     m_operation = op;