Refactor os specific code for x86 (both 32 and 64 bit).

Move Linux specific code into ${arch}/Gos-linux.c
diff --git a/include/libunwind-common.h.in b/include/libunwind-common.h.in
index 9005a6c..228460a 100644
--- a/include/libunwind-common.h.in
+++ b/include/libunwind-common.h.in
@@ -220,6 +220,7 @@
 #define unw_set_fpreg		UNW_OBJ(set_fpreg)
 #define unw_get_save_loc	UNW_OBJ(get_save_loc)
 #define unw_is_signal_frame	UNW_OBJ(is_signal_frame)
+#define unw_handle_signal_frame	UNW_OBJ(handle_signal_frame)
 #define unw_get_proc_name	UNW_OBJ(get_proc_name)
 #define unw_set_caching_policy	UNW_OBJ(set_caching_policy)
 #define unw_regname		UNW_ARCH_OBJ(regname)
@@ -246,6 +247,7 @@
 extern int unw_set_fpreg (unw_cursor_t *, int, unw_fpreg_t);
 extern int unw_get_save_loc (unw_cursor_t *, int, unw_save_loc_t *);
 extern int unw_is_signal_frame (unw_cursor_t *);
+extern int unw_handle_signal_frame (unw_cursor_t *);
 extern int unw_get_proc_name (unw_cursor_t *, char *, size_t, unw_word_t *);
 extern const char *unw_strerror (int);