cmake: Drop ENABLE_SDL_GPU option

The code conditionals using SDL_gpu in the source tree are unmaintained
and likely broken. From past discussions with vultraz and Aginor, the
plan ahead is to completely drop SDL_gpu and its support code once
there's no risk of conflict with certain WIP branches.

CMakeLists.txt

@@ -53,7 +53,6 @@ option(ENABLE_TESTS "Build unit tests")
 option(ENABLE_NLS "Enable building of translations" ON)
 option(ENABLE_LOW_MEM "Reduce memory usage by removing extra functionality" OFF)
 option(ENABLE_OMP "Enables OpenMP, and has additional dependencies" OFF)
-option(ENABLE_SDL_GPU "Enable building with SDL_gpu (experimental)" OFF)
 option(ENABLE_LIBPNG "Enable support for writing png files (screenshots, images)" ON)
 option(ENABLE_LIBINTL "Enable using libintl for translations instead of Boost.Locale library (not recommended)" OFF)
 option(ENABLE_HISTORY "Enable using GNU history for history in lua console" ON)

src/CMakeLists.txt

@@ -43,14 +43,6 @@ if(ZLIB_INCLUDE_DIR)
 	include_directories(SYSTEM ${ZLIB_INCLUDE_DIR} )
 endif()
 
-if(ENABLE_SDL_GPU)
-	message(STATUS "Configuring SDL_gpu...")
-	add_definitions("-DSDL_GPU")
-	add_subdirectory(SDL_gpu)
-	set(sdl_gpu-lib-vc SDL_gpu.lib)
-	set(sdl_gpu-lib SDL_gpu)
-endif(ENABLE_SDL_GPU)
-
 # needed to get include paths in the subfolders correct
 include_directories( ${CMAKE_SOURCE_DIR}/src/ )
 # needed to have the generated config.h used, too
@@ -70,7 +62,6 @@ if(MSVC)
 		${sdl-lib}
 		${sdlmain-lib}
 		ws2_32.lib
-		${sdl_gpu-lib-vc}
 	)
 else(MSVC)
 	set(common-external-libs
@@ -78,7 +69,6 @@ else(MSVC)
 		${Boost_IOSTREAMS_LIBRARY}
 		${Boost_REGEX_LIBRARY}
 		${Boost_PROGRAM_OPTIONS_LIBRARY}
-		${sdl_gpu-lib}
 	)
 endif(MSVC)