link atomic library automatic when compile on raspberrypi (#1405)

* 增加检测atomic源文件

* 支持树莓派编译，自动检测atomic链接库

* 精简cmake操作

CMakeLists.txt

@@ -25,6 +25,18 @@ if (CMAKE_SYSTEM_NAME MATCHES "Linux")
     SET(LIBRARY_OUTPUT_PATH ${RELEASE_DIR}/linux/${CMAKE_BUILD_TYPE})
     SET(EXECUTABLE_OUTPUT_PATH ${RELEASE_DIR}/linux/${CMAKE_BUILD_TYPE})
     add_compile_options(-fPIC -Wall -Wno-unused-variable -Wno-unused-value)
+    INCLUDE(CheckCXXSourceCompiles)
+    file(READ ${CMAKE_CURRENT_SOURCE_DIR}/cmake/checks/atomic_check.cpp atomic_check_cpp)
+    CHECK_CXX_SOURCE_COMPILES("${atomic_check_cpp}" HAVE_CXX_ATOMICS_WITHOUT_LIB)
+    if(NOT HAVE_CXX_ATOMICS_WITHOUT_LIB)
+        list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
+        CHECK_CXX_SOURCE_COMPILES("${atomic_check_cpp}" HAVE_CXX_ATOMICS_WITH_LIB)
+        if(NOT HAVE_CXX_ATOMICS_WITH_LIB)
+            message(WARNING "Compiler doesn't support std::atomic<long long>")
+        else()
+            set(CMAKE_CXX_LINK_FLAGS "${CMAKE_CXX_LINK_FLAGS} -latomic")
+        endif()
+    endif()
 elseif (CMAKE_SYSTEM_NAME MATCHES "Windows")
     if (CMAKE_CL_64)
         set(CL_32_64 64)

cmake/checks/atomic_check.cpp

+#include <atomic>
+
+static int test()
+{
+    std::atomic<long long> x;
+    return x;
+}
+
+int main()
+{
+    return test();
+}
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