Detect the host system and architecture at configure time, makes conditional compiling easier. Start the platform defines cleanup, there's still much left. Autodetect the number of cores for every platform (BSD is untested), the port mantainers should drop their own implementations.

git-svn-id: https://svn.code.sf.net/p/desmume/code/trunk@4821 5577840e-afb3-4e59-9ef3-2b7f898b1952
Oops, that was unintended.

git-svn-id: https://svn.code.sf.net/p/desmume/code/trunk@4822 5577840e-afb3-4e59-9ef3-2b7f898b1952
fix windows compiling

git-svn-id: https://svn.code.sf.net/p/desmume/code/trunk@4823 5577840e-afb3-4e59-9ef3-2b7f898b1952