(partially) Fix Bug#55227 Fix compiler warnings in innodb with gcc 4.6

Fix compiler warnings:
btr/btr0cur.c: In function 'btr_store_big_rec_extern_fields':
btr/btr0cur.c:3368:10: error: variable 'rec_page' set but not used [-Werror=unused-but-set-variable]
btr/btr0cur.c: In function 'btr_free_externally_stored_field':
btr/btr0cur.c:3542:8: error: variable 'offset' set but not used [-Werror=unused-but-set-variable]
btr/btr0cur.c:3539:10: error: variable 'rec_page' set but not used [-Werror=unused-but-set-variable]

storage/innobase/btr/btr0cur.c

@@ -3365,7 +3365,9 @@ btr_store_big_rec_extern_fields(
 	page_t*	page;
 	ulint	space_id;
 	page_t*	prev_page;
+#ifdef UNIV_SYNC_DEBUG
 	page_t*	rec_page;
+#endif /* UNIV_SYNC_DEBUG */
 	ulint	prev_page_no;
 	ulint	hint_page_no;
 	ulint	i;
@@ -3460,7 +3462,10 @@ btr_store_big_rec_extern_fields(
 
 			extern_len -= store_len;
 
-			rec_page = buf_page_get(space_id,
+#ifdef UNIV_SYNC_DEBUG
+			rec_page =
+#endif /* UNIV_SYNC_DEBUG */
+			buf_page_get(space_id,
 				     buf_frame_get_page_no(data),
 				     RW_X_LATCH, &mtr);
 #ifdef UNIV_SYNC_DEBUG
@@ -3536,10 +3541,11 @@ btr_free_externally_stored_field(
 					X-latch to the index tree */
 {
 	page_t*	page;
+#ifdef UNIV_SYNC_DEBUG
 	page_t*	rec_page;
+#endif /* UNIV_SYNC_DEBUG */
 	ulint	space_id;
 	ulint	page_no;
-	ulint	offset;
 	ulint	extern_len;
 	ulint	next_page_no;
 	ulint	part_len;
@@ -3556,7 +3562,10 @@ btr_free_externally_stored_field(
 	for (;;) {
 		mtr_start(&mtr);
 
-		rec_page = buf_page_get(buf_frame_get_space_id(data),
+#ifdef UNIV_SYNC_DEBUG
+		rec_page =
+#endif /* UNIV_SYNC_DEBUG */
+		buf_page_get(buf_frame_get_space_id(data),
 			     buf_frame_get_page_no(data),
 			     RW_X_LATCH, &mtr);
 #ifdef UNIV_SYNC_DEBUG
@@ -3568,8 +3577,6 @@ btr_free_externally_stored_field(
 		page_no = mach_read_from_4(data + local_len
 					   + BTR_EXTERN_PAGE_NO);
 
-		offset = mach_read_from_4(data + local_len
-					  + BTR_EXTERN_OFFSET);
 		extern_len = mach_read_from_4(data + local_len
 					      + BTR_EXTERN_LEN + 4);