Split ogl_get_verinfo() into ogl_tune_for_current() and
ogl_extensions_init(), and consolidate all the OpenGL extension handling
into ogl_extensions.cpp. Unify the code paths for texture anisotropy and
GPU synchronization for OpenGL and OpenGL ES.
Currently, our renderer only uses GLES 1.0, so no real world implementation
will support sync objects for such an old context, but the logic is valid,
and this way, the GLES specific code paths are reduced.
This patch also fixes an issue where the old ogl_get_verinfo() did modify
the texture filtering mode if no anisotropic filter was available. This
was some leftover from the time when the anisotropic filter was a just
a specific CGameConfig.TexFilt mode, and not a separate, orthogonal setting
CGameCfg.TexAnisotropy that it is now.
The new OGL extension code included <SDL/SDL.h>, which works when the
SDL headers are installed in a directory named SDL and that directory is
in a system search directory. Those conditions usually hold on Linux,
both for /usr/include and /usr/local/include. However, non-Linux users
sometimes install SDL in other places. Kreator reports that the OGL
build on OS X failed because his SDL headers were on the search path,
but not in a directory named SDL on the search path. Switch the
include directive to an unqualified name to match other SDL includes.
Reported-by: kreatordxx <private mail>
Fixes: db267af6f2 ("add basic OpenGL extension handling")
