[patch 0/2] PR49847: Add hook to place read-only lookup-tables in named address-space

[Georg-Johann Lay]

For some targets, the best place to put read-only lookup tables as
generated by -ftree-switch-conversion is not the generic address space
but some target specific address space.

This is the case for AVR, where for most devices .rodata must be
located in RAM.

Part #1 adds a new, optional target hook that queries the back-end
about the desired address space.  There is currently only one user:
tree-switch-conversion.c::build_one_array() which re-builds value_type
and array_type if the address space returned by the backend is not
the generic one.

Part #2 is the AVR part that implements the new hook and adds some
sugar around it.