Browse postgresql source code in clion Follow

I want to set up postgres source code locally in CLion so that I can browse it. But clion doesn't understand include clauses. It looks like this:

I've tried pretty much everything I could find by "postgres" + "clion" search term combination, but still no luck. I bet it has something to do with includes specified in CMakeLists.txt. I tried the following options:

cmake_minimum_required(VERSION 3.6)
project(postgres)

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")

add_custom_target(postgres COMMAND make -C ${postgres_SOURCE_DIR})

and

cmake_minimum_required(VERSION 3.6)
project(postgres)


set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")

include_directories (${postgres_INCLUDE_DIRS})
link_directories(${postgres_LIBRARY_DIRS})

add_custom_target(postgres COMMAND make -C ${postgres_SOURCE_DIR})

and

cmake_minimum_required(VERSION 3.6)
project(postgres)


set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")

include_directories(SYSTEM./src)

add_custom_target(postgres COMMAND make -C ${postgres_SOURCE_DIR})

and a bunch of other options, but, yeah, still no luck.

The situation is complicated by the fact that I'm totally unfamiliar with C ecosystem, so I'm sorry if I'm being dumb.