add alternative tcc bootstrap path

[cosinusoidally]

This is a draft PR that adds my alternative bootstrap path for tcc https://github.com/fosslinux/live-bootstrap/issues/355 . I've marked this as a draft as it is probably not yet in a state suitable for merging (eg I updated the ci to unconditionally enable the flag --tcc_bootstrap_alt but probably both the mes and tcc_bootstrap_alt path need testing automatically via ci). I also had some issues with nested conditionals in kaem that meant I needed to add some awkward combined conditionals (which also currently have bug that will break architectures other than x86/riscv). There may be a better way of doing that.