[cmake] add missing files (#4112)

src/core/CMakeLists.txt

@@ -178,6 +178,9 @@ set(COMMON_SOURCES
     utils/child_supervision.cpp
     utils/heap.cpp
     utils/jam_detector.cpp
+    utils/missing_strlcat.c
+    utils/missing_strlcpy.c
+    utils/missing_strnlen.c
     utils/parse_cmdline.cpp
     utils/slaac_address.cpp
 )