Hardened allocator designed for modern systems. It has integration into Android's Bionic libc and can be used externally with musl and glibc as a dynamic library for use on other Linux-based platforms. It will gain more portability / integration over time.
It was added 3 years ago as a workaround for old clang versions in 58b56f10eae3a16d34ac4123f56fa90c8100cce6
Thanks to @zanthed for helping investigating this.