rustdoc: port the -C option from rustc#49956

Merged

bors merged 4 commits intorust-lang:masterfrom

QuietMisdreavus:rustdoc-codegen

Apr 16, 2018

Commits on Apr 11, 2018

add target features when extracting and running doctests
QuietMisdreavus
committed

Commits on Apr 12, 2018

add test for using target features in doctests
QuietMisdreavus
committed

Commits on Apr 13, 2018