Fixed compilation error when trying to compile libmysqld on powermac


configure.in:
  Added flag if __cxa_pure_virtual() should be defined.
  Without this flag, we get a warning from my_global.h for every compiled file on powermacg5
extra/yassl/taocrypt/include/type_traits.hpp:
  Avoid compiler warning
include/my_global.h:
  Avoid compiler warning on powermacg5
sql/mysqld.cc:
  Fix compiler error when compiling embedded on powermac