Fix wasi::fs::OpenOptions to imply write when append is on
Fix wasi::fs::OpenOptions to imply write when append is on

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