bootstrap: don't call support_xz in hot-path
bootstrap: don't call support_xz in hot-path

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