-# "no" by default, can be set to "yes" if a target
-# wishes to use __cxa_atexit() by default if the
-# $enable___cxa_atexit variable is not set.
+# The default value for the $enable___cxa_atexit
+# variable. enable___cxa_atexit needs to be set to
+# "yes" for the correct operation of C++ destructors
+# but it relies upon the presence of a non-standard C
+# library function called __cxa_atexit.
+# Since not all C libraries provide __cxa_atexit the
+# default value of $default_use_cxa_atexit is set to
+# "no" except for targets which are known to be OK.