Move buffer to top-level as it's not audio only.

Makefile

@@ -67,7 +67,7 @@ ifeq ($(HAVE_PULSE), 1)
 endif
 
 ifeq ($(HAVE_SDL), 1)
-   OBJ += gfx/sdl.o gfx/gl.o input/sdl.o audio/sdl.o audio/buffer.o
+   OBJ += gfx/sdl.o gfx/gl.o input/sdl.o audio/sdl.o fifo_buffer.o
    DEFINES += $(SDL_CFLAGS)
    LIBS += $(SDL_LIBS)
 ifeq ($(OSX),1)

Makefile.win32

@@ -37,7 +37,7 @@ else
 endif
 
 ifeq ($(HAVE_SDL), 1)
-   OBJ += gfx/sdl.o gfx/gl.o input/sdl.o audio/sdl.o audio/buffer.o
+   OBJ += gfx/sdl.o gfx/gl.o input/sdl.o audio/sdl.o fifo_buffer.o
    LIBS += $(SDL_LIBS) -lopengl32
    DEFINES += $(SDL_CFLAGS) -DHAVE_SDL
 endif

Makefile.win64

@@ -36,7 +36,7 @@ else
 endif
 
 ifeq ($(HAVE_SDL), 1)
-   OBJ += gfx/sdl.o gfx/gl.o input/sdl.o audio/sdl.o audio/buffer.o
+   OBJ += gfx/sdl.o gfx/gl.o input/sdl.o audio/sdl.o fifo_buffer.o
    LIBS += $(SDL_LIBS) -lopengl32 
    DEFINES += $(SDL_CFLAGS) -DHAVE_SDL
 endif

audio/rsound.c

@@ -19,7 +19,7 @@
 #include "driver.h"
 #include <stdlib.h>
 #include <rsound.h>
-#include "buffer.h"
+#include "fifo_buffer.h"
 #include <stdbool.h>
 #include "SDL.h"
 

audio/sdl.c

@@ -27,7 +27,7 @@
 #include "SDL_audio.h"
 #include "SDL_thread.h"
 #include "general.h"
-#include "buffer.h"
+#include "fifo_buffer.h"
 
 typedef struct sdl_audio
 {

fifo_buffer.c

@@ -13,7 +13,7 @@
  *  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#include "buffer.h"
+#include "fifo_buffer.h"
 
 struct fifo_buffer
 {