Move platform-specific thread code into common thread/ folder

Makefile.xenon

@@ -18,7 +18,7 @@ PPU_TARGET_ADJUSTED := retroarch-libxenon.elf32
 LDDIRS = -L. -L$(DEVKITXENON)/usr/lib -L$(DEVKITXENON)/xenon/lib/32
 INCDIRS = -I. -I$(DEVKITXENON)/usr/include
 
-OBJ = fifo_buffer.o retroarch.o driver.o file.o file_path.o settings.o message.o rewind.o movie.o gfx/gfx_common.o patch.o compat/compat.o screenshot.o audio/hermite.o dynamic.o audio/utils.o conf/config_file.o 360/frontend-xenon/main.o 360/xenon360_audio.o 360/xenon360_input.o 360/xenon360_video.o
+OBJ = fifo_buffer.o retroarch.o driver.o file.o file_path.o settings.o message.o rewind.o movie.o gfx/gfx_common.o patch.o compat/compat.o screenshot.o audio/hermite.o dynamic.o audio/utils.o conf/config_file.o 360/frontend-xenon/main.o 360/xenon360_audio.o 360/xenon360_input.o 360/xenon360_video.o thread/xenon_sdl_threads.o
 
 LIBS = -lretro_xenon360 -lxenon -lm -lc
 DEFINES = -std=gnu99 -DHAVE_CONFIGFILE=1 -DPACKAGE_VERSION=\"0.9.7-rc1\" -DRARCH_CONSOLE -DHAVE_GETOPT_LONG=1 -Dmain=rarch_main

thread.c

@@ -22,7 +22,7 @@
 #elif defined(_XBOX)
 #include <xtl.h>
 #elif defined(GEKKO)
-#include "gx/gx_pthread.h"
+#include "thread/gx_pthread.h"
 #else
 #include <pthread.h>
 #include <time.h>