Skip function_telemetry.c when telemetry is disabled

This avoids allocating the telemetry hash table, which saves a little
shared memory.

src/loader/CMakeLists.txt

@@ -4,9 +4,12 @@ set(SOURCES
     bgw_counter.c
     bgw_launcher.c
     bgw_interface.c
-    function_telemetry.c
     lwlocks.c)
 
+if(USE_TELEMETRY)
+  list(APPEND SOURCES function_telemetry.c)
+endif()
+
 set(TEST_SOURCES ${PROJECT_SOURCE_DIR}/test/src/symbol_conflict.c)
 
 add_library(${PROJECT_NAME}-loader MODULE ${SOURCES})

src/loader/loader.c

@@ -37,7 +37,9 @@
 #include "loader/bgw_interface.h"
 #include "loader/bgw_launcher.h"
 #include "loader/bgw_message_queue.h"
+#ifdef USE_TELEMETRY
 #include "loader/function_telemetry.h"
+#endif
 #include "loader/loader.h"
 #include "loader/lwlocks.h"
 
@@ -546,7 +548,9 @@ timescaledb_shmem_startup_hook(void)
 	ts_bgw_counter_shmem_startup();
 	ts_bgw_message_queue_shmem_startup();
 	ts_lwlocks_shmem_startup();
+#ifdef USE_TELEMETRY
 	ts_function_telemetry_shmem_startup();
+#endif
 }
 
 /*
@@ -565,7 +569,9 @@ timescaledb_shmem_request_hook(void)
 	ts_bgw_counter_shmem_alloc();
 	ts_bgw_message_queue_alloc();
 	ts_lwlocks_shmem_alloc();
+#ifdef USE_TELEMETRY
 	ts_function_telemetry_shmem_alloc();
+#endif
 }
 
 static void