Auto merge of #5058 - sfackler:patch-2, r=Mark-Simulacrum
Auto merge of #5058 - sfackler:patch-2, r=Mark-Simulacrum

Update default codegen-units

It's been 16 since rustc 1.24.

tsurai/cargo,vojtechkral/cargo,vojtechkral/cargo,vojtechkral/cargo,rust-lang/cargo,nipunn1313/cargo,tshepang/cargo,rustyhorde/cargo,rust-lang/cargo,rust-lang/cargo,nipunn1313/cargo,rustyhorde/cargo,tshepang/cargo,eminence/cargo,tsurai/cargo,rustyhorde/cargo,eminence/cargo,eminence/cargo,vojtechkral/cargo,tsurai/cargo,nipunn1313/cargo,rustyhorde/cargo,tshepang/cargo,tshepang/cargo,tsurai/cargo,eminence/cargo,tsurai/cargo,nipunn1313/cargo,rust-lang/cargo