xmlpool: 'promote' LOCALEDIR variable

xmlpool: 'promote' LOCALEDIR variable

This is the only place in mesa that uses this constuct which seems
to be GNUmake-ism. Attempting to build with POSIX make implementations
(bmake) would fail as below.

--- options.h ---
LOCALEDIR := .
sh: line 2: LOCALEDIR: command not found
*** [options.h] Error code 127

So let's keep things consistent and compatible by making the variable
non target specific.

v2:
 - Bring back LOCALEDIR.
 - Reword the commit message
 - Change mesa-stable tag 10.6 > 11.0

Cc: 11.0 <mesa-stable@lists.freedesktop.org>
Cc: Jonathan Gray <jsg@jsg.id.au>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>