lib, glibc: Get rid of withTLS

glibc removed the underlying flag in 2011 in
83cd14204559abbb52635006832eaf4d2f42514a [1].

This gets us one step closer to fixing #34274: the cross stdenv for
aarch64-unknown-linux-gnu at least evals now.

Thanks to @Dezgeg for doing all the research for this.

[1]: https://sourceware.org/git/?p=glibc.git;a=commit;h=83cd14204559abbb52635006832eaf4d2f42514a