If it has been defined (by "configure", in "include/my_config.h"),
then an "#undef" is needed to avoid a redefinition.

This is needed to prevent a compile error of the debug server on AIX.


mysys/mf_keycache.c:
  It may happen, that "include/my_config.h" already contains a
    #define inline ...
  as created by "configure" (this happens on AIX).
  In this case, an "#undef" is needed to avoid a compile error.