-mno-tls-direct-seg-refs support in glibc for i386 PV Xen

[Florian Weimer <fweimer@redhat.com>]

I'm about to remove nosegneg support from upstream glibc, special builds
that use -mno-tls-direct-seg-refs, and the ability load different
libraries built in this mode automatically, when the Linux kernel tells
us to do that.  I think the intended effect is that these special builds
do not use operands of the form %gs:(%eax) when %eax has the MSB set
because that had a performance hit with paravirtualization on 32-bit
x86.  Instead, the thread pointer is first loaded from %gs:0, and the
actual access does not use a segment prefix.

Before doing that, I'd like to ask if anybody is still using this
feature?

I know that we've been carrying nosegneg libraries for many years, in
some cases even after we stopped shipping 32-bit kernels. 8-/ The
feature has always been rather poorly documented, and the way the
dynamic loader selects those nosegneg library variants is still very
bizarre.

Thanks,
Florian