Glibc on arm has a memory tagging option that can be enabled
via GLIBC_TUNABLES="glibc.mem.tagging=$SOMETHING" when glibc
is built with memory tagging support and the kernel/HW supports
MTE. This should be side effect free unless the user turns it
on with approprate HW support.
Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>