1. Like with gcc's `ld`, also use the `group_start` code to create a
2. xc16 tricked into believing the 'link_whole' was about `--*-group`,
but it should use gcc's `--whole-archive` instead.
3. Not clear what the get_lib_prefix should really do, but for picolibc
it seems I want just `''`.
The problem with picolibc was that the `-l` would be prefixed to a lib
like `picolib/libm/libm.a`. Though of course the `-l` would be necessary
for just a plain `m` (that's what I assumed this would be used for).
I think this might need some clarification from the meson devs ;-)