The linkname directive, //go:linkname localname [importpath.name], now optionally allows one-argument forms. Details found in compiler directives document. There was also a TODO in linkname.go to check for any additional arguments. The os package had a new insert-link to net that needed to be ignored and handled in the native overrides.

• I reorganized the parseGoLinknames method to separate it into:
  • reading the linkname from the comment
  • checking if the linkname is supported by GopherJS
• I added two methods to check for known links to ignore:
  • one method is for specific var-links
  • one method is for specific insert-links or any insert-links in specific packages
• I added the native override for net.newUnixFile

The introduction of the one-argument form (and the new part in the compiler directives document) makes me feel like there will be more insert-style links on the horizon since the one-argument is to "suppresses the usual error for a function that lacks a body." So by having a better way to deal with specific links when needed, we will be able to track new insert-links and var-links better.

If enough insert-links are added we will probably have to start handling them directly instead of ignoring them and handling them in the native overrides. However, that's seems to be outside of the scope of this PR and #1270.