[Ohrrpgce] SVN: teeemcee/9969 Add SDL2.dll (official build v2.0.7) and fix gfx_sdl2 not compiling

[subversion at HamsterRepublic.com]

teeemcee
2018-01-19 02:40:40 -0800 (Fri, 19 Jan 2018)
305
Add SDL2.dll (official build v2.0.7) and fix gfx_sdl2 not compiling

SDL2 is under the zlib license. It does not require mentioning SDL2
in materials distributed with binaries.
SDL1.2 is under LGPL. Technically, we should add the copyright info
for it, and other code/libraries we use, to our LICENSE.txt.
---
A   wip/SDL2.dll
U   wip/gfx_sdl2.bas
A   wip/support/README-SDL.txt
U   wip/unicode.bi