Managed to only have tcc+musl as binary seed, as expected (that include the sources, which are all unpacked, tar nor any decompressors are bootstrapped yet), current sizes with grabbing them from gentoo-musl:
27M /tmp/initramfs-tcc.cpio 4.5M /tmp/initramfs-tcc.cpio.xzLikely could get even smaller with grabbing Alpine packages (-O2 -ggdb doesn't yields the smallest binaries), and it's with both libc.so and libc.a from musl for now.