Auto merge of #4638 - efyang:docs-cc, r=alexcrichton
Auto merge of #4638 - efyang:docs-cc, r=alexcrichton

Update docs to use cc instead of gcc

Closes #4626.

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