Add option to build libsystemd automatically as integral part of sdbus-c++

cmake/LibsystemdExternalProject.cmake

@@ -0,0 +1,46 @@
+find_program(MESON meson)
+find_program(NINJA ninja)
+
+if((NOT MESON) OR (NOT NINJA))
+    message(FATAL_ERROR "Meson and Ninja are required to build libsystemd")
+endif()
+
+find_library(GLIBC_RT_LIBRARY rt)
+find_package(PkgConfig REQUIRED)
+pkg_check_modules(MOUNT REQUIRED mount)
+pkg_check_modules(CAP REQUIRED libcap)
+if (NOT CAP_FOUND)
+    find_library(CAP_LIBRARIES cap) # Compat with Ubuntu 14.04 which ships libcap w/o .pc file
+endif()
+
+set(LIBSYSTEMD_VERSION v239 CACHE STRING "libsystemd version (>=v239) to build and incorporate into libsdbus-c++")
+
+if(NOT CMAKE_BUILD_TYPE)
+    set(LIBSYSTEMD_BUILD_TYPE "plain")
+elseif(CMAKE_BUILD_TYPE STREQUAL "Debug")
+    set(LIBSYSTEMD_BUILD_TYPE "debug")
+else()
+    set(LIBSYSTEMD_BUILD_TYPE "release")
+endif()
+
+include(ExternalProject)
+ExternalProject_Add(LibsystemdBuildProject
+                    PREFIX libsystemd
+                    GIT_REPOSITORY https://github.com/systemd/systemd.git
+                    GIT_TAG        ${LIBSYSTEMD_VERSION}
+                    UPDATE_COMMAND ""
+                    CONFIGURE_COMMAND ${CMAKE_COMMAND} -E remove <BINARY_DIR>/*
+                              COMMAND ${MESON} --buildtype=${LIBSYSTEMD_BUILD_TYPE} -Dstatic-libsystemd=pic <SOURCE_DIR> <BINARY_DIR>
+                    BUILD_COMMAND ${NINJA} -C <BINARY_DIR> libsystemd.a
+                    INSTALL_COMMAND ""
+                    LOG_DOWNLOAD 1 LOG_UPDATE 1 LOG_CONFIGURE 1 LOG_BUILD 1)
+
+ExternalProject_Get_property(LibsystemdBuildProject SOURCE_DIR)
+set(SYSTEMD_INCLUDE_DIRS ${SOURCE_DIR}/src)
+ExternalProject_Get_property(LibsystemdBuildProject BINARY_DIR)
+set(SYSTEMD_LIBRARY_DIRS ${BINARY_DIR})
+
+#add_library(libsystemd-static STATIC IMPORTED)
+#set_target_properties(libsystemd-static PROPERTIES IMPORTED_LOCATION ${SYSTEMD_LIBRARY_DIRS}/libsystemd.a)
+#target_link_libraries(libsystemd-static ${MOUNT_LIBRARIES} ${CAP_LIBRARIES} ${GLIBC_RT_LIBRARY})
+set(SYSTEMD_LIBRARIES ${SYSTEMD_LIBRARY_DIRS}/libsystemd.a ${MOUNT_LIBRARIES} ${CAP_LIBRARIES} ${GLIBC_RT_LIBRARY})