Add support for building on/cross-compiling the shared library for Windows and OS X

Also ensure that the shared library is versioned, and an implib is created on
Windows.
Introduce little endian RISC support

Little endian RISC support was either not or incorrectly implemented in AES.
This was avoided by always depending on the CICS implementations for LE.
These additions and fixes add the LE RISC support in AES and allow configure
to set the conditions for it.
Merge pull request #86 from nirbheek/master

Add support for cross-compiling the shared library for Windows and OS X.  Thanks for the contribution.
Fix bug from pull request #86 where the pc file was being deleted when doing a clean.
Change the autoconf input file along with configure itself

Need to make the changes in both the committed configure and configure.in
Merge pull request #89 from JaapKeuter/aes_risc_le

Introduce little endian RISC support.  Thanks for the contribution.