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

Fix compiler warning:
btr/btr0btr.c: In function 'btr_page_split_and_insert':
btr/btr0btr.c:1898:11: error: variable 'insert_page' set but not used [-Werror=unused-but-set-variable]

storage/innodb_plugin/btr/btr0btr.c

@@ -1895,7 +1895,6 @@ btr_page_split_and_insert(
 	buf_block_t*	left_block;
 	buf_block_t*	right_block;
 	buf_block_t*	insert_block;
-	page_t*		insert_page;
 	page_cur_t*	page_cursor;
 	rec_t*		first_rec;
 	byte*		buf = 0; /* remove warning */
@@ -2153,8 +2152,6 @@ insert_empty:
 		insert_block = right_block;
 	}
 
-	insert_page = buf_block_get_frame(insert_block);
-
 	/* 7. Reposition the cursor for insert and try insertion */
 	page_cursor = btr_cur_get_page_cur(cursor);
 
@@ -2166,8 +2163,12 @@ insert_empty:
 
 #ifdef UNIV_ZIP_DEBUG
 	{
+		page_t*		insert_page
+			= buf_block_get_frame(insert_block);
+
 		page_zip_des_t*	insert_page_zip
 			= buf_block_get_page_zip(insert_block);
+
 		ut_a(!insert_page_zip
 		     || page_zip_validate(insert_page_zip, insert_page));
 	}