commit.h: rearrange 'index' to shrink struct commit

On linux 64-bit architecture, pahole finds that there's a 4 bytes
padding after 'index'. Moving it to the end reduces this struct's size
from 72 to 64 bytes (because of another 4 bytes padding after
graph_pos). On linux 32-bit, the struct size remains 52 bytes like
before.

Signed-off-by: Nguyễn Thái Ngọc Duy <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pclouds

commit.h

@@ -19,11 +19,11 @@ struct commit_list {
 struct commit {
 	struct object object;
 	void *util;
-	unsigned int index;
 	timestamp_t date;
 	struct commit_list *parents;
 	struct tree *tree;
 	uint32_t graph_pos;
+	unsigned int index;
 };
 
 extern int save_commit_buffer;