Fix compilation errors after clang modules checkin.

llvm-svn: 223484
diff --git a/lldb/source/Expression/ClangModulesDeclVendor.cpp b/lldb/source/Expression/ClangModulesDeclVendor.cpp
index 6eebea2..dc07ac7 100644
--- a/lldb/source/Expression/ClangModulesDeclVendor.cpp
+++ b/lldb/source/Expression/ClangModulesDeclVendor.cpp
@@ -7,9 +7,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "ClangModulesDeclVendor.h"
-
 #include "lldb/Core/StreamString.h"
+#include "lldb/Expression/ClangModulesDeclVendor.h"
 #include "lldb/Host/FileSpec.h"
 #include "lldb/Host/Host.h"
 #include "lldb/Host/HostInfo.h"
@@ -23,6 +22,8 @@
 #include "clang/Sema/Lookup.h"
 #include "clang/Serialization/ASTReader.h"
 
+#include <mutex>
+
 using namespace lldb_private;
 
 namespace {