mscoree: Implement semi-stub for _CorValidateImage.

[Michael Müller]

Am 25.08.2015 um 18:24 schrieb Vincent Povirk:
> Why do we set the entry point to 0 on 64-bit and _CorDllMain or
> _CorExeMain on 32-bit?
> 
> 

The entry point is a DWORD in IMAGE_OPTIONAL_HEADER64. If the
mscoree.dll is not loaded within a 32 bit memory range of the image,
there is no way to specify the correct entry point. This should also
match the windows behavior.