CMakeLists 增加 OpenMP 的支持

1. CMakeLists 增加如下：

find_package(OpenMP REQUIRED)
if(OpenMP_FOUND)
    message(STATUS "found openmp") 
    set(CMAKE_C_FLAGS ${CMAKE_C_FLAGS}, ${OPENMP_C_FLAGS})
    set(CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS}, ${OPENMP_CXX_FLAGS})
else()
    message(FATAL_ERROR "openmp not found!")
endif()

2. C++ 代码中增加头文件

#include 

3. 调用的地方，增加宏

		#pragma omp parallel for
		for (int id_y = 0; id_y < num_samples_y; ++id_y) 
		{
			
		}

4. 其他

如果平台不支持 OpenMP，会自动降级成串行执行；