musl toolchain:

musl, GCC, binutils, GMP, MPFR, MPC, Linux, and ISL (optional).

Bootstrap process:

Build 1 --
Build musl-bootstrap with available binaries in OBS.
Build gcc-cross-musl against musl-bootstrap and libc++ with available binaries in OBS.
Build 1 is not full-featured and its binary is not ideal.

Build 2 --
Build musl, libc++, binutils, GMP, MPFR, MPC, Linux and optionally ISL with build 1.
Build GCC-musl against musl and libc++ with build 1.
Build 2 is full-featured and with ideal binary.