[clang][deps] Add missing include

Discovered by https://green.lab.llvm.org/job/llvm.org/job/clang-stage2-Rthinlto/588.

(cherry picked from commit da1c19a)

Author: jansvoboda11

clang/include/clang/Tooling/DependencyScanning/InProcessModuleCache.h

@@ -12,6 +12,7 @@
 #include "clang/Serialization/ModuleCache.h"
 #include "llvm/ADT/StringMap.h"
 
+#include <mutex>
 #include <shared_mutex>
 
 namespace clang {