CMake: fetch and build dependencies

Using cmake to fetch and build instead of using git submodule.

FetchContent

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include(FetchContent)
set(FETCHCONTENT_QUIET FALSE)
FetchContent_Declare(log4cplus
GIT_REPOSITORY https://github.com/log4cplus/log4cplus.git
GIT_TAG REL_2_0_6
GIT_PROGRESS TRUE
)
FetchContent_MakeAvailable(log4cplus)
add_dependencies(log4cplus)
target_link_libraries(${PROJECT_NAME} PRIVATE log4cplus)

ExternalProject

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include(ExternalProject)

function (build_external_project TARGET ARGS GIT_REPOSITORY GIT_TAG)

set(trigger_build_dir ${CMAKE_BINARY_DIR}/force_${TARGET})

#mktemp dir in build tree
file(MAKE_DIRECTORY ${trigger_build_dir} ${trigger_build_dir}/build)

#generate false dependency project
set(CMAKE_LIST_CONTENT "
cmake_minimum_required(VERSION 3.14)
include(ExternalProject)
ExternalProject_add(${TARGET}
GIT_REPOSITORY ${GIT_REPOSITORY}
GIT_TAG ${GIT_TAG}
CMAKE_ARGS ${ARGS}
TEST_COMMAND \"\"
)
add_custom_target(trigger_${TARGET})
add_dependencies(trigger_${TARGET} ${TARGET})
")
message(STATUS "CMAKE_ARGS is ${CMAKE_ARGS}")
file(WRITE ${trigger_build_dir}/CMakeLists.txt "${CMAKE_LIST_CONTENT}")

execute_process(COMMAND ${CMAKE_COMMAND} ..
WORKING_DIRECTORY ${trigger_build_dir}/build
)
execute_process(COMMAND ${CMAKE_COMMAND} --build .
WORKING_DIRECTORY ${trigger_build_dir}/build
)

endfunction()

build_external_project(log4cplus
"-DCMAKE_INSTALL_PREFIX=${MY_INSTALL_DIR} -DLOG4CPLUS_BUILD_TESTING=OFF -DBUILD_SHARED_LIBS=OFF"
https://github.com/log4cplus/log4cplus.git
REL_2_0_6
)