Update CMake files to account for new location of Threading.cpp.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73708 91177308-0d34-0410-b5e6-96231b3b80d8

lib/System/CMakeLists.txt

@@ -12,6 +12,7 @@ add_llvm_library(LLVMSystem
   Program.cpp
   RWMutex.cpp
   Signals.cpp
+  Threading.cpp
   TimeValue.cpp
   )