https://cmake.org/cmake/help/latest/module/FindThreads.html

在子文件夹中的CMakeList.txt：

aux_source_directory(. DIR_SUB_SRCS)
add_library(echatlib SHARED ${DIR_SUB_SRCS}) # STATIC SHARED# 方法一
find_package(Threads REQUIRED)
target_link_libraries (echatlib Threads::Threads) #echatlib PUBLIC Threads::Threads# 方法二，效果和方法一相同
find_package(Threads)
target_link_libraries (echatlib ${CMAKE_THREAD_LIBS_INIT})