linux-headers-5.2 and proper use of SIOCGSTAMP

[Sergei Trofimovich]

Commit https://github.com/torvalds/linux/commit/0768e17073dc527ccd18ed5f96ce85f9985e9115
("net: socket: implement 64-bit timestamps") caused a bit of userspace breakage
for existing programs:
- firefox: https://bugs.gentoo.org/689808
- qemu: https://lists.sr.ht/~philmd/qemu/%3C20190604071915.288045-1-borntraeger%40de.ibm.com%3E
- linux-atm: https://gitweb.gentoo.org/repo/gentoo.git/tree/net-dialup/linux-atm/files/linux-atm-2.5.2-linux-5.2-SIOCGSTAMP.patch?id=408621819a85bf67a73efd33a06ea371c20ea5a2

I have a question: how a well-behaved app should include 'SIOCGSTAMP'
definition to keep being buildable against old and new linux-headers?

'man 7 socket' explicitly mentions SIOCGSTAMP and mentions only
    #include <sys/socket.h>
as needed header.

Should #include <linux/sockios.h> always be included by user app?
Or should glibc tweak it's definition of '#include <sys/socket.h>'
to make it available on both old and new version of linux headers?

CCing both kernel and glibc folk as I don't understand on which
side issue should be fixed.

Thanks!

-- 

  Sergei