glibc: backport MTE improvements from master

After realising that the MTE support in 2.33 was suboptimal, discussion with
upstream revealed that these issues are known and already fixed.

They will be in glibc 2.34 which is scheduled for August, so backport the
fixes for now.

(From OE-Core rev: e5eadbf45b7fb953c557438854b0a96ba740c589)

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>