I don't see anything to suggest that Arch uses eglibc. The glibc package in the repos is clearly the original glibc (look at the name, package URL, and build config) and there is no other package named "eglibc". Also, a very recent forum post[1] implies eglibc is not the standard.
Wikipedia says[2] that Arch uses eglibc, but their source is the eglibc website home page and I find no such claim on the entire site. I can't find anything about eglibc on the Arch mailing list, either.
Have I missed something?
[0]: https://www.archlinux.org/packages/core/x86_64/glibc/