adds the SDL2 library as a subrepository that is automatically configured and built with the rest of ogredeps via CMake's ExternalProject macro
fix MinGW builds, which could not handle the Windows 8 Kit headers.
allow 64-bit MinGW builds, which were unable to build zzlib and FreeImage.
These were done together since MinGW is my primary build platform and the SDL2 changes would not have been fully tested with MinGW without the included changes.
I have tested these changes using Visual Studio 2013 and MinGW (32 and 64-bit via TDM-GCC). I have not yet had a chance to test on Mac, but will do so in the next few days.
From commit notes for adding SDL2:
SDL2 will be used as the default input for a near-future OGRE SampleBrowser,
will be used by one of the primary OGRE windowing system, and is used by the
recently released AZDO branch of OGRE for samples.
SDL2 is added as a Mercurial subrepo, while CMake configures and installs
it using the ExternalProject macro. Since SDL2 is not aware of the Release/Debug
folder structure used by ogredeps, files are moved after installation by CMake.
DirectX is no longer required on WIN32 since SDL2 does not require it.
OIS will not be available when DirectX is not found.
From commit for fixing MinGW builds and adding 64-bit MinGW support:
MinGW cannot handle Windows Kit 8 headers, so skip them.
zzip incorrectly used _MSC_VER precompiler flags to indicate WIN32,
which led to wrong blocks being evaluated for MINGW builds.
PluginTIFF has a precision error from a typecasted return from libtiff.
While not really solved here, does at least allow 64-bit MinGW builds.