Move the autoupdater launcher into its own public domain source file.

So other games can steal this piece if they want.

Makefile

@@ -1694,6 +1694,7 @@ Q3OBJ = \
   $(B)/client/sdl_snd.o \
   \
   $(B)/client/con_log.o \
+  $(B)/client/sys_autoupdater.o \
   $(B)/client/sys_main.o
 
 ifdef MINGW
@@ -2230,6 +2231,7 @@ Q3DOBJ = \
   $(B)/ded/null_snddma.o \
   \
   $(B)/ded/con_log.o \
+  $(B)/ded/sys_autoupdater.o \
   $(B)/ded/sys_main.o
 
 ifeq ($(ARCH),x86)