While LLVM/Clang has been self-hosted for years -- going back to 2010 -- the Embedded LLVM Compiler Collection only reached that milestone this week. ELLCC was self-hosted by using GCC to build the compiler wirh standard Linux support, use ECC to build itself with libc++ and against its ABI along with libunwind, musl, and Compiler-RT. Lastly, the newly built ECC compiler was then used to rebuild the same code-base configuration.
The Embedded LLVM Compiler Collection adapts Clang and LLVM to focus on multi-target cross-compilation support for embedded systems. ELLCC is still considered to be pre-release software but supports architectures like ARM and x86 but also MIPS, PowerPC, Microblaze, and NIOS2.
More information on ELLCC is available from the project site. The self-hosting news was shared on the LLVM mailing list.