improve `filesearch::get_or_default_sysroot` r=ozkanonur
improve `filesearch::get_or_default_sysroot` r=ozkanonur

Signed-off-by: Onur Özkan <e274eeff768c6396088ec6eb091f4bf4d47ab1e0@onurozkan.dev>

rust-lang/miri,rust-lang/miri,rust-lang/miri,rust-lang/miri