Compilation fails on `compiler_builtin` v0.1.18

[0ndorio]

It seems like the latest update of compiler_builtin to v0.1.18 got us in a situation where it is no longer possible to build for the xtensa-esp32-none-elf target.

The issue appears due to the line assert!(stack_required) of classify_arg_ty() in src/librustc_target/abi/call/xtensa.rs.

the stack trace

thread 'rustc' panicked at 'assertion failed: stack_required', src/librustc_target/abi/call/xtensa.rs:78:9
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
   1: std::sys_common::backtrace::print
   2: std::panicking::default_hook::{{closure}}
   3: std::panicking::default_hook
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
   6: std::panicking::begin_panic
   7: rustc_target::abi::call::xtensa::classify_arg_ty
   8: rustc_target::abi::call::xtensa::compute_abi_info
   9: <rustc_target::abi::call::FnType<'tcx, &'tcx rustc::ty::TyS<'tcx>> as rustc_codegen_llvm::abi::FnTypeExt<'tcx>>::adjust_for_abi
  10: <rustc_target::abi::call::FnType<'tcx, &'tcx rustc::ty::TyS<'tcx>> as rustc_codegen_llvm::abi::FnTypeExt<'tcx>>::new
  11: rustc_codegen_llvm::declare::<impl rustc_codegen_ssa::traits::declare::DeclareMethods<'tcx> for rustc_codegen_llvm::context::CodegenCx<'ll, 'tcx>>::declare_fn
  12: rustc_codegen_llvm::mono_item::<impl rustc_codegen_ssa::traits::declare::PreDefineMethods<'tcx> for rustc_codegen_llvm::context::CodegenCx<'ll, 'tcx>>::predefine_fn
  13: rustc_codegen_ssa::mono_item::MonoItemExt::predefine
  14: rustc_codegen_llvm::base::compile_codegen_unit::module_codegen
  15: rustc::dep_graph::graph::DepGraph::with_task
  16: rustc_codegen_llvm::base::compile_codegen_unit
  17: rustc_codegen_ssa::base::codegen_crate
  18: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_utils::codegen_backend::CodegenBackend>::codegen_crate
  19: rustc::util::common::time
  20: rustc_driver::driver::phase_4_codegen
  21: <std::thread::local::LocalKey<T>>::with
  22: rustc::ty::context::TyCtxt::create_and_enter
  23: rustc_driver::driver::compile_input
  24: <scoped_tls::ScopedKey<T>>::set
  25: rustc_driver::run_compiler
  26: <scoped_tls::ScopedKey<T>>::set
  27: syntax::with_globals
  28: __rust_maybe_catch_panic
  29: <F as alloc::boxed::FnBox<A>>::call_box
  30: std::sys_common::thread::start_thread
  31: std::sys::unix::thread::Thread::new::thread_start
  32: start_thread
  33: __clone
query stack during panic:
end of query stack

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.34.0-dev running on x86_64-unknown-linux-gnu

note: compiler flags: -Z force-unstable-if-unmarked -C opt-level=3 -C codegen-units=1 -C target-cpu=esp32 -C save-temps -C link-arg=-nostdlib -C link-arg=-ucall_user_start_cpu0 -C link-arg=-u__cxa_guard_dummy -C link-arg=-u__cxx_fatal_exception -C link-arg=-uld_include_panic_highint_hdl -C link-arg=-uesp_app_desc -C link-arg=-Wl,--gc-sections -C link-arg=-Wl,-static -C link-arg=-Wl,--start-group -C link-arg=-Lbuild/app_update -C link-arg=-lapp_update -C link-arg=-Lbuild/driver -C link-arg=-ldriver -C link-arg=-Lbuild/esp-tls -C link-arg=-lesp-tls -C link-arg=-Lbuild/esp32 -C link-arg=-lesp32 -C link-arg=esp-idf/components/esp32/libhal.a -C link-arg=-Lesp-idf/components/esp32/lib -C link-arg=-lcore -C link-arg=-Lesp-idf/components/esp32/ld -C link-arg=-Tesp32_out.ld -C link-arg=-Tbuild/esp32/esp32.project.ld -C link-arg=-Tesp32.rom.ld -C link-arg=-Tesp32.peripherals.ld -C link-arg=-Tesp32.rom.libgcc.ld -C link-arg=-Tesp32.rom.spiram_incompatible_fns.ld -C link-arg=-Lbuild/esp_ringbuf -C link-arg=-lesp_ringbuf -C link-arg=-Lbuild/freertos -C link-arg=-lfreertos -C link-arg=-Wl,--undefined=uxTopUsedPriority -C link-arg=-Lbuild/heap -C link-arg=-lheap -C link-arg=-Lbuild/log -C link-arg=-llog -C link-arg=esp-idf/components/newlib/lib/libc.a -C link-arg=esp-idf/components/newlib/lib/libm.a -C link-arg=-Lbuild/newlib -C link-arg=-lnewlib -C link-arg=-Lbuild/pthread -C link-arg=-lpthread -C link-arg=-Lbuild/soc -C link-arg=-lsoc -C link-arg=-Lbuild/spi_flash -C link-arg=-lspi_flash -C link-arg=-Lbuild/vfs -C link-arg=-lvfs -C link-arg=-Lbuild/xtensa-debug-module -C link-arg=-lxtensa-debug-module -C link-arg=-lgcc -C link-arg=-lstdc++ -C link-arg=-lgcov -C link-arg=-Wl,--end-group -C link-arg=-Wl,-EL --crate-type lib

note: some of the compiler flags provided by cargo are hidden

error: Could not compile `compiler_builtins`.

Some debug output I could inject:

[src/librustc_target/abi/call/xtensa.rs:70] arg.layout.details = LayoutDetails {
    variants: Single {
        index: 0
    },
    fields: Arbitrary {
        offsets: [
            Size {
                raw: 0
            },
            Size {
                raw: 16
            }
        ],
        memory_index: [
            0,
            1
        ]
    },
    abi: ScalarPair(
        Scalar {
            value: Int(
                I128,
                true
            ),
            valid_range: 0..=340282366920938463463374607431768211455
        },
        Scalar {
            value: Int(
                I8,
                false
            ),
            valid_range: 0..=1
        }
    ),
    align: AbiAndPrefAlign {
        abi: Align {
            pow2: 3
        },
        pref: Align {
            pow2: 3
        }
    },
    size: Size {
        raw: 24
    }
}
[src/librustc_target/abi/call/xtensa.rs:71] xlen = 32
[src/librustc_target/abi/call/xtensa.rs:72] remaining_gpr = 0
[src/librustc_target/abi/call/xtensa.rs:74] arg_size.bits() = 192
[src/librustc_target/abi/call/xtensa.rs:75] MAX_ARG_IN_REGS_SIZE = 128

[0ndorio]

Fixed by #3.