Add check if submodules need to be updated

Adds CMake check that pulls from the different git remotes and checks if
there is any output.

CMakeLists.txt

@@ -172,6 +172,25 @@ else()
   message(STATUS "Building without build tag")
 endif()
 
+if(NOT MANUAL_SUBMODULES)
+  find_package(Git)
+  if(GIT_FOUND)
+    message(STATUS "Checking submodules")
+    execute_process(COMMAND bash -c "cd ${CMAKE_CURRENT_SOURCE_DIR}/external/miniupnp && git rev-parse HEAD" OUTPUT_VARIABLE miniupnpLocalHead WORKING_DIRECTORY ${CMAKE_SOURCE_DIR})
+    execute_process(COMMAND bash -c "cd ${CMAKE_CURRENT_SOURCE_DIR}/external/unbound && git rev-parse HEAD" OUTPUT_VARIABLE unboundLocalHead WORKING_DIRECTORY ${CMAKE_SOURCE_DIR})
+    execute_process(COMMAND bash -c "cd ${CMAKE_CURRENT_SOURCE_DIR}/external/rapidjson && git rev-parse HEAD" OUTPUT_VARIABLE rapidjsonLocalHead WORKING_DIRECTORY ${CMAKE_SOURCE_DIR})
+    execute_process(COMMAND bash -c "git ls-tree HEAD ${CMAKE_CURRENT_SOURCE_DIR}/external/miniupnp | awk '{print $3}'" OUTPUT_VARIABLE miniupnpCheckedHead WORKING_DIRECTORY ${CMAKE_SOURCE_DIR})
+    execute_process(COMMAND bash -c "git ls-tree HEAD ${CMAKE_CURRENT_SOURCE_DIR}/external/unbound | awk '{print $3}'" OUTPUT_VARIABLE unboundCheckedHead WORKING_DIRECTORY ${CMAKE_SOURCE_DIR})
+    execute_process(COMMAND bash -c "git ls-tree HEAD ${CMAKE_CURRENT_SOURCE_DIR}/external/rapidjson | awk '{print $3}'" OUTPUT_VARIABLE rapidjsonCheckedHead WORKING_DIRECTORY ${CMAKE_SOURCE_DIR})
+    string(COMPARE EQUAL "${miniupnpLocalHead}" "${miniupnpCheckedHead}" miniupnpUpToDate)
+    string(COMPARE EQUAL "${unboundLocalHead}" "${unboundCheckedHead}" unboundUpToDate)
+    string(COMPARE EQUAL "${rapidjsonLocalHead}" "${rapidjsonCheckedHead}" rapidjsonUpToDate)
+    if (NOT miniupnpUpToDate OR NOT unboundUpToDate OR NOT rapidjsonUpToDate)
+      message(FATAL_ERROR "Submodules not up to date. Please update with git subdmoule init && git submodule update, or run cmake with -DMANUAL_SUBMODULES=1")
+    endif()
+  endif()
+endif()
+
 set(CMAKE_C_FLAGS_RELEASE "-DNDEBUG ${OPT_FLAGS_RELEASE}")
 set(CMAKE_CXX_FLAGS_RELEASE "-DNDEBUG ${OPT_FLAGS_RELEASE}")