Rollup merge of #38264 - ollie27:rustdoc_src_macro, r=brson
Rollup merge of #38264 - ollie27:rustdoc_src_macro, r=brson

rustdoc: Remove broken src links from reexported items from macros

When an item is defined in an external macro it doesn't get a real
filename so we need to filter out these when generating src links for
reexported items.

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