I don't know of any embedded systems still using glibc.

Dietlibc, uclibc (used by openwrt and the other consumer router replacement firmwares), musl libc, and bionic (since Android is technically an embedded Linux, so should be mentioned as well) dominate the embedded Linux space.

I do embedded development and I use Glibc on all of our products. It's as simple as checking the box in Buildroot, so why not? The version of Glibc I am using has special accelerated memcpy and string functions for my CPU (e6500 PPC, Altivec).

OpenEmbedded / Yocto / whatever (it's complicated) uses glibc, and that's a quite popular distribution construction kit.

I'm no expert, but at least STM32's default is newlib or newlib-nano, which it inherits from the ARM GCC toolchain[1] from what I gather. I just checked and here it's defined as the following by default:

    #define _TIME_T_ __int_least64_t   
    typedef _TIME_T_ time_t;

[1]: https://imagecraft.com/blog/2019/04/embedded-gcc-libraries-n...

BeagleBoneBlack Debian:

ldd --version ldd (Debian GLIBC 2.28-10) 2.28 Copyright (C) 2018 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. Written by Roland McGrath and Ulrich Drepper.

And of course, on actual microcontrollers newlib-nano is what you're likely using with a GNU toolchain.

I don't remember ever being involved with embedded not using glibc if it was using any sort of Linux.

OpenWrt uses musl for some years now.