When we are showing symbol info for a macro or a function
in a c file, then add a link to search the source code
of that macro/function in codesearch.debian.net .

It uses the codesearch.debian.net regex search with the
following regex which looks up source definitions for C
macros and functions:

(?mi:^(?:#define\s+)?func_name)\s*\((?m:([^;]+)$)