kani-compiler panic on unimplemented scalar

[tedinski]

Reproduction:

git clone https://github.com/bitflags/bitflags
cd bitflags
RUST_BACKTRACE=1 cargo kani --enable-unstable --only-codegen assess

Result:

thread '<unnamed>' panicked at 'not implemented', kani-compiler/src/codegen_cprover_gotoc/codegen/operand.rs:419:18
stack backtrace:
   3: kani_compiler::codegen_cprover_gotoc::codegen::operand::<impl kani_compiler::codegen_cprover_gotoc::context::goto_ctx::GotocCtx>::codegen_scalar
             at /home/ubuntu/rmc/kani-compiler/src/codegen_cprover_gotoc/codegen/operand.rs:419:18
   4: kani_compiler::codegen_cprover_gotoc::codegen::operand::<impl kani_compiler::codegen_cprover_gotoc::context::goto_ctx::GotocCtx>::codegen_single_variant_single_field
             at /home/ubuntu/rmc/kani-compiler/src/codegen_cprover_gotoc/codegen/operand.rs:438:22

The code in question is a remaining raw unimplemented in codegen_scalar:

kani/kani-compiler/src/codegen_cprover_gotoc/codegen/operand.rs

Line 419 in 5680dac

_ => unimplemented!(),

[carolynzech]

The codegen_scalar function doesn't exist anymore, and with Kani v0.62.0 at commit bitflags/bitflags@80684fd I can clone the repo, add an extern crate kani at the top (c.f. #3906), and run cargo kani without issue.