pthreads 在系统上工作：
$ gcc -o what what.c
/tmp/ccI6m52b.o: In function `main':
what.c:(.text+0x37): undefined reference to `pthread_create'
what.c:(.text+0x48): undefined reference to `pthread_join'
collect2: error: ld returned 1 exit status
$ gcc -pthread -o what what.c
$ ./what
In the thread.
但是，当我cmake使用以下系统运行时CMakeLists.txt：
cmake_minimum_required(VERSION 2.8.6)
FIND_PACKAGE (Threads)
输出是：
-- Could NOT find Threads (missing: Threads_FOUND)
是什么赋予了？错误日志状态：
/usr/bin/cc -std=c11 -D_GNU_SOURCE -Wall -Wextra -Wpointer-arith -Wundef -Wvla -Wwrite-strings -Werror -Wno-error=extra -Wno-error=deprecated-declarations -Wno-error=sign-compare -Wno-error=strict-aliasing -Wno-error=type-limits -Wno-unused-parameter -Wno-error=unused-variable -Wno-error=undef -Wno-error=uninitialized -Wlogical-op -Wno-error=maybe-uninitialized -Waggregate-return -Wnested-externs …