cmake_minimum_required(VERSION 3.9)
project(libossia CXX)
set(CMAKE_CXX_FLAGS "-std=c++17 ${CMAKE_CXX_FLAGS}")
find_package(Threads REQUIRED)

causes

-- The CXX compiler identification is AppleClang 9.0.0.9000039
-- Check for working CXX compiler: /Library/Developer/CommandLineTools/usr/bin/c++
-- Check for working CXX compiler: /Library/Developer/CommandLineTools/usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Looking for C++ include pthread.h
-- Looking for C++ include pthread.h - not found
CMake Error at /usr/local/Cellar/cmake/3.10.2/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:137 (message):
  Could NOT find Threads (missing: Threads_FOUND)
Call Stack (most recent call first):
  /usr/local/Cellar/cmake/3.10.2/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:378 (_FPHSA_FAILURE_MESSAGE)
  /usr/local/Cellar/cmake/3.10.2/share/cmake/Modules/FindThreads.cmake:205 (FIND_PACKAGE_HANDLE_STANDARD_ARGS)
  CMakeLists.txt:5 (find_package)
-- Configuring incomplete, errors occurred!
See also "/tmp/tutu/tata/CMakeFiles/CMakeOutput.log".
See also "/tmp/tutu/tata/CMakeFiles/CMakeError.log".
[1]    37429 exit 1     cmake ..

CMake 3.10.2 on macOS 10.13.1 with latest Xcode.