build fails when cross compiling because of autoconf and rpl_malloc

If pycrypto was cross compiled it can result in the following error:

>>> from Crypto import Random
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
    from Crypto import Random
  File "/usr/local/lib/python2.7/site-packages/Crypto/Random/__init__.py", line 29, in <module>
    from Crypto.Random import _UserFriendlyRNG
  File "/usr/local/lib/python2.7/site-packages/Crypto/Random/_UserFriendlyRNG.py", line 38, in <module>
    from Crypto.Random.Fortuna import FortunaAccumulator
  File "/usr/local/lib/python2.7/site-packages/Crypto/Random/Fortuna/FortunaAccumulator.py", line 39, in <module>
    import FortunaGenerator
  File "/usr/local/lib/python2.7/site-packages/Crypto/Random/Fortuna/FortunaGenerator.py", line 36, in <module>
    from Crypto.Cipher import AES
  File "/usr/local/lib/python2.7/site-packages/Crypto/Cipher/AES.py", line 50, in <module>
    from Crypto.Cipher import _AES
ImportError: /usr/local/lib/python2.7/site-packages/Crypto/Cipher/_AES.so: undefined symbol: rpl_malloc

This is because autoconf assumes the target architecture during a cross compile won't have a gnu compatible malloc replaces malloc() calls with rpl_malloc() calls. The client code needs define rpl_malloc() as a wrapper around malloc() as explained here:

http://wiki.buici.com/xwiki/bin/view/Programing+C+and+C%2B%2B/Autoconf+and+RPL_MALLOC

And the actual autoconf documentation here:

http://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.69/html_node/Particular-Functions.html#index-AC_005fFUNC_005fMALLOC-453

A work-around is to set the environment variable "ac_cv_func_malloc_0_nonnull" to "yes" during the ./configure step (although if the target system really doesn't have a gnu compliant malloc then I think you could have a problem).