Provide source location support for systemd_sink.h

tests/CMakeLists.txt

@@ -14,7 +14,7 @@ set(SPDLOG_UTESTS_SOURCES
     test_mpmc_q.cpp
     test_sink.h
     test_fmt_helper.cpp
-	test_stdout_api.cpp)
+    test_stdout_api.cpp)
 
 file(MAKE_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/logs")
 enable_testing()

tests/test_systemd.cpp

@@ -8,6 +8,6 @@ TEST_CASE("systemd", "[all]")
     spdlog::logger logger("spdlog_systemd_test", systemd_sink);
 
     logger.debug("test debug");
-    logger.error("test error");
+    SPDLOG_LOGGER_ERROR((&logger), "test error");
     logger.info("test info");
 }