emulator: opengl: Avoid conflicts with SDL_CONFIG

Do not redefine SDL_CONFIG to avoid conflicts with the emulator's
build system which depend on its definition. Note that this has
been fixed in another patch (https://review.source.android.com/25684)
but it is also cleaner to do this here.

Change-Id: I1a30d200e467ac7a91a1e6135fa1de34033e8df0
2 files changed