[PATCH] Linux: Add gettid system call wrapper [BZ #6399]

[Joseph Myers]

On Wed, 5 Dec 2018, Florian Weimer wrote:

> This commit adds gettid to <unistd.h> on Linux, and not to the
> kernel-independent GNU API.

This is missing a NEWS entry, and documentation (which seems particularly 
important in this case, to discuss what a tid is and is not and what 
interfaces it can be used with).

-- 
Joseph S. Myers
joseph@codesourcery.com