Merge pull request #3157 from apple/compnerd/static

Update CMakeLists.txt

Author: millenomi

CMakeLists.txt

@@ -55,6 +55,10 @@ include(XCTest)
 
 set(CF_DEPLOYMENT_SWIFT YES CACHE BOOL "Build for Swift" FORCE)
 
+set(CMAKE_THREAD_PREFER_PTHREAD TRUE)
+set(THREADS_PREFER_PTHREAD_FLAG OFF)
+find_package(Threads REQUIRED)
+
 set(SAVED_BUILD_SHARED_LIBS ${BUILD_SHARED_LIBS})
 set(BUILD_SHARED_LIBS NO)
 add_subdirectory(CoreFoundation EXCLUDE_FROM_ALL)