问如何使用cmake包含静态库？

EN

#CMakeLists.txt
cmake_minimum_required(VERSION 3.0.0)
project(cpptest VERSION 0.1.0)

include(CTest)
enable_testing()

add_executable(cpptest main.cpp)

set(CPACK_PROJECT_NAME ${PROJECT_NAME})
set(CPACK_PROJECT_VERSION ${PROJECT_VERSION})
include(CPack)

target_link_libraries(cpptest "${CMAKE_SOURCE_DIR}/libixwebsocket.a")

//main.cpp
#include <iostream>
#include <ixwebsocket/IXNetSystem.h>
#include <ixwebsocket/IXWebSocket.h>

int main(int, char**) {
    std::cout << "Hello, world!\n";

    ix::WebSocket webSocket;
}

[build] [ 50%] Linking CXX executable cpptest
[build] /usr/bin/ld: ../libixwebsocket.a(IXWebSocket.cpp.o): in function `ix::WebSocket::start()':
[build] IXWebSocket.cpp:(.text+0x2240): undefined reference to `pthread_create'
ld] /usr/bin/ld: ../libixwebsocket.a(IXWebSocket.cpp.o): in function `ix::WebSocket::checkConnection(bool)':
[build] IXWebSocket.cpp:(.text+0x5b8d): undefined reference to `pthread_cond_clockwait'
[build] /usr/bin/ld: ../libixwebsocket.a(IXWebSocketPerMessageDeflateCodec.cpp.o): in function `bool ix::WebSocketPerMessageDeflateCompressor::compressData<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&) [clone .part.0]':
[build] IXWebSocketPerMessageDeflateCodec.cpp:(.text+0x67): undefined reference to `deflate'
[build] /usr/bin/ld: ../libixwebsocket.a(IXWebSocketPerMessageDeflateCodec.cpp.o): in function `ix::WebSocketPerMessageDeflateCompressor::~WebSocketPerMessageDeflateCompressor()':
[build] IXWebSocketPerMessageDeflateCodec.cpp:(.text+0x35c): undefined reference to `deflateEnd'
[build] /usr/bin/ld: ../libixwebsocket.a(IXWebSocketPerMessageDeflateCodec.cpp.o): in function `ix::WebSocketPerMessageDeflateCompressor::init(unsigned char, bool)':
[build] IXWebSocketPerMessageDeflateCodec.cpp:(.text+0x3a6): undefined reference to `deflateInit2_'
[build] /usr/bin/ld: ../libixwebsocket.a(IXWebSocketPerMessageDeflateCodec.cpp.o): in function `ix::WebSocketPerMessageDeflateDecompressor::~WebSocketPerMessageDeflateDecompressor()':
[build] IXWebSocketPerMessageDeflateCodec.cpp:(.text+0x64c): undefined reference to `inflateEnd'
[build] /usr/bin/ld: ../libixwebsocket.a(IXWebSocketPerMessageDeflateCodec.cpp.o): in function `ix::WebSocketPerMessageDeflateDecompressor::init(unsigned char, bool)':
[build] IXWebSocketPerMessageDeflateCodec.cpp:(.text+0x685): undefined reference to `inflateInit2_'
[build] /usr/bin/ld: ../libixwebsocket.a(IXWebSocketPerMessageDeflateCodec.cpp.o): in function `ix::WebSocketPerMessageDeflateDecompressor::decompress(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&)':
[build] IXWebSocketPerMessageDeflateCodec.cpp:(.text+0x7d6): undefined reference to `inflate'
[build] /usr/bin/ld: ../libixwebsocket.a(IXWebSocketPerMessageDeflateCodec.cpp.o): in function `bool ix::WebSocketPerMessageDeflateCompressor::compressData<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<unsigned char, std::allocator<unsigned char> > >(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::vector<unsigned char, std::allocator<unsigned char> >&) [clone .part.0]':
[build] IXWebSocketPerMessageDeflateCodec.cpp:(.text+0x90d): undefined reference to `deflate'
[build] /usr/bin/ld: ../libixwebsocket.a(IXSocketOpenSSL.cpp.o): in function `ix::SocketOpenSSL::openSSLInitialize()':
[build] IXSocketOpenSSL.cpp:(.text+0x1c): undefined reference to `OPENSSL_init_ssl'
[build] /usr/bin/ld: IXSocketOpenSSL.cpp:(.text+0x29): undefined reference to `OPENSSL_init_ssl'