Reminder: Document _BSD_SOURCE and _SVID_SOURCE transition to _DEFAULT_SOURCE.

Michael,

This is a reminder so we all don't forget that _BSD_SOURCE and _SVID_SOURCE are transitioning to _DEFAULT_SOURCE.

I have documented them here under:

"3.2.2. Deprecation of _BSD_SOURCE and _SVID_SOURCE feature macros"
https://sourceware.org/glibc/wiki/Release/2.20#Packaging_Changes

We should say something in the manual pages about this transition.

If you've got time please feel free to crib any and all of the text from that section. I wrote it all and I'm contributing it to the linux kernel man pages project as GPLv2.

Cheers,
Carlos.