Tools: ensure ESP32 malloc is wrapped to zero memory

The relevant linker flag needed to be put in the CMake script.

Tools/ardupilotwaf/boards.py

@@ -1390,6 +1390,7 @@ class linux(Board):
         ]
 
         # wrap malloc to ensure memory is zeroed
+        # note that this also needs to be done in the CMakeLists.txt files
         env.LINKFLAGS += ['-Wl,--wrap,malloc']
 
         if cfg.options.force_32bit: