链接GMP库时出错

我有以下CMakeList.txt

cmake_minimum_required(VERSION 2.8)
set(CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}")
find_package(GMP REQUIRED)
add_executable(Turrial main.cpp)

与以下简单的源文件main.cpp

#include <iostream>
#include <gmp.h>
#include <cstdio>

using namespace std;
int main(){ 
    mpz_t a,b;
    mpz_init_set_str(a,"45",10);
    mpz_init_set_str(b,"12",10);
    mpz_add(a,a,b);
    cout <<mpz_get_str(NULL,10,a)<<endl;    
    }

我包含了我在网上找到的FindGMP.cmake文件：

set(GMP_PREFIX "" CACHE PATH "path ")


find_path(GMP_INCLUDE_DIR gmp.h gmpxx.h 
    PATHS ${GMP_PREFIX}/include /usr/include /usr/local/include )

find_library(GMP_LIBRARY NAMES gmp libgmp 
    PATHS ${GMP_PREFIX}/lib /usr/lib /usr/local/lib)


if(GMP_INCLUDE_DIR AND GMP_LIBRARY)
    get_filename_component(GMP_LIBRARY_DIR ${GMP_LIBRARY} PATH)
    set(GMP_FOUND TRUE)
endif()

if(GMP_FOUND)
   if(NOT GMP_FIND_QUIETLY)
      MESSAGE(STATUS "Found GMP: ${GMP_LIBRARY}")
   endif()
elseif(GMP_FOUND)
   if(GMP_FIND_REQUIRED)
      message(FATAL_ERROR "Could not find GMP")
   endif()
endif(

当我运行cmake时，我有以下输出：

moyle@localhost:~/Desktop/gmptri$ cmake .
-- Found GMP: /usr/local/lib/libgmp.so
-- Configuring done
-- Generating done
-- Build files have been written to: /home/moyle/Desktop/gmptri

然后我运行make并得到以下错误：

  (precise)moyle@localhost:~/Desktop/gmptri$ make VERBOSE=1
/usr/bin/cmake -H/home/moyle/Desktop/gmptri -B/home/moyle/Desktop/gmptri --check-build-system CMakeFiles/Makefile.cmake 0
/usr/bin/cmake -E cmake_progress_start /home/moyle/Desktop/gmptri/CMakeFiles /home/moyle/Desktop/gmptri/CMakeFiles/progress.marks
make -f CMakeFiles/Makefile2 all
make[1]: Entering directory `/home/moyle/Desktop/gmptri'
make -f CMakeFiles/Turrial.dir/build.make CMakeFiles/Turrial.dir/depend
make[2]: Entering directory `/home/moyle/Desktop/gmptri'
cd /home/moyle/Desktop/gmptri && /usr/bin/cmake -E cmake_depends "Unix Makefiles" /home/moyle/Desktop/gmptri /home/moyle/Desktop/gmptri /home/moyle/Desktop/gmptri /home/moyle/Desktop/gmptri /home/moyle/Desktop/gmptri/CMakeFiles/Turrial.dir/DependInfo.cmake --color=
make[2]: Leaving directory `/home/moyle/Desktop/gmptri'
make -f CMakeFiles/Turrial.dir/build.make CMakeFiles/Turrial.dir/build
make[2]: Entering directory `/home/moyle/Desktop/gmptri'
Linking CXX executable Turrial
/usr/bin/cmake -E cmake_link_script CMakeFiles/Turrial.dir/link.txt --verbose=1
/usr/bin/c++       CMakeFiles/Turrial.dir/main.cpp.o  -o Turrial -rdynamic 
CMakeFiles/Turrial.dir/main.cpp.o: In function `main':
main.cpp:(.text+0x1a): undefined reference to `__gmpz_init_set_str'
main.cpp:(.text+0x30): undefined reference to `__gmpz_init_set_str'
main.cpp:(.text+0x47): undefined reference to `__gmpz_add'
collect2: ld returned 1 exit status
make[2]: *** [Turrial] Error 1
make[2]: Leaving directory `/home/moyle/Desktop/gmptri'
make[1]: *** [CMakeFiles/Turrial.dir/all] Error 2
make[1]: Leaving directory `/home/moyle/Desktop/gmptri'
make: *** [all] Error 2

谁能帮我？