Remove builddeps: win32/gmp win64/gmp win32/sdl win64/sdl
Revert "Update Windows 32 bit SDL build dependency to 2.0.10" This reverts commit d2cdd999d3d7214b2da17099df63b3b409b0ae23.
Upgrade to SDL 2.0.5.
Update Windows SDL to 2.0.4.
Win64: switch to using SDL2.