Auto merge of #28562 - llogiq:shootout, r=alexcrichton
Auto merge of #28562 - llogiq:shootout, r=alexcrichton

Since 1.3.0 the BufWriter has seen tremendous speedups. So when I use it in the shootout benchmarks, I see some nice speedup (which up to 1.2.0 was nixed by the pessimizations during initialization).

graydon/rust,GBGamer/rust,aidancully/rust,graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,GBGamer/rust,graydon/rust,aidancully/rust,graydon/rust,GBGamer/rust,GBGamer/rust,graydon/rust