[Bug target/120933] Turn on -mtls-dialect=gnu2 by default on x86-64

[sjames at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120933

--- Comment #9 from Sam James <sjames at gcc dot gnu.org> ---
Do we want to implement an auto mode later?

r16-3355-g96a291c4 doesn't change the default, but allows distributions to do
it easily. We could check whether ld emits GLIBC_ABI_GNU_TLS or
GLIBC_ABI_GNU2_TLS to decide the default.

Then per richi's comment
(https://inbox.sourceware.org/gcc/cafiyyc3helvt1yhp3d8bnqsdhfr6t3-jq4izxf5varcqbdv...@mail.gmail.com/)
if I understand it right, it's on integrators to change it back if they need to
for other compatibility reasons.

I don't know if by "change the default" he meant "change it back if they need
to" or "change it at all". I hope he meant the former.