[Bug c/69480] Bad error message on assigning to read-only

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69480

--- Comment #2 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
This error happens after lhs is c_fully_fold()-ed, thus what %qE prints is a
symbolic representation of GCC's IR and no what the user wrote. Pretty-printing
is the root of all evil (PR35441, PR49152).