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/SymbolFile/DWARF/SymbolFileDWARF.cpp b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
index e3e5b7c..a2c466a 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -1619,7 +1619,7 @@
 bool
 SymbolFileDWARF::CompleteType (CompilerType &compiler_type)
 {
-    lldb_private::Mutex::Locker locker(GetObjectFile()->GetModule()->GetMutex());
+    std::lock_guard<std::recursive_mutex> guard(GetObjectFile()->GetModule()->GetMutex());
 
     ClangASTContext *clang_type_system = llvm::dyn_cast_or_null<ClangASTContext>(compiler_type.GetTypeSystem());
     if (clang_type_system)