Add links to codegen docs for rustc synonym flags
Add links to codegen docs for rustc synonym flags

The rustc "-g" and "-o" fags are synonyms of the "-c" codegen flags.
This adds a link to the codegen docs for each synonym.

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