Modify CMake to check out a given PyBind11 version upon configuration…

… from zip file

CMakeLists.txt

@@ -19,6 +19,8 @@ set(BUILD_SHARED_LIBS ON)
 set(CMAKE_POSITION_INDEPENDENT_CODE ON)
 set(CMAKE_CXX_STANDARD 17)
 
+set(PYBIND_SUBMODULE_COMMIT 435dbdd)
+
 foreach(WARN ${COMPILER_WARN})
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -W${WARN}")       
 endforeach()
@@ -134,8 +136,11 @@ if(PYTHONLIBS_FOUND)
                 execute_process(COMMAND git init WORKING_DIRECTORY ${PROJECT_SOURCE_DIR} OUTPUT_QUIET ERROR_QUIET)
                 execute_process(COMMAND rm -Rf ${PROJECT_SOURCE_DIR}/external/pybind11 OUTPUT_QUIET ERROR_QUIET)
                 execute_process(COMMAND git submodule add -f https://github.com/pybind/pybind11 external/pybind11 WORKING_DIRECTORY ${PROJECT_SOURCE_DIR} OUTPUT_QUIET ERROR_QUIET)
+                execute_process(COMMAND git checkout ${PYBIND_SUBMODULE_COMMIT} WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}/external/pybind11 OUTPUT_QUIET ERROR_QUIET)
+                execute_process(COMMAND git submodule update --init --recursive WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}/external/pybind11 OUTPUT_QUIET ERROR_QUIET)
+            else()
+                execute_process(COMMAND git submodule update --init --recursive WORKING_DIRECTORY ${PROJECT_SOURCE_DIR} OUTPUT_QUIET ERROR_QUIET)
             endif()
-            execute_process(COMMAND git submodule update --init --recursive WORKING_DIRECTORY ${PROJECT_SOURCE_DIR} OUTPUT_QUIET ERROR_QUIET)
             if(NOT EXISTS ${PROJECT_SOURCE_DIR}/external/pybind11/CMakeLists.txt)
                 message(ERROR "pybind11 download failure.")
             else()