Rollup merge of #45338 - ishitatsuyuki:boot-jemalloc, r=aidanhs
Rollup merge of #45338 - ishitatsuyuki:boot-jemalloc, r=aidanhs

bootstrap: Avoid fetching jemalloc if it's disabled

Fix #45300

More conditions, more madness :) Tested locally.

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