Found unstable fingerprints for exported_symbols with custom target

First of all, this is known issue (unstable fingerprints, https://github.com/rust-lang/rust/issues/84970), I'm just adding another case.

### Code

1. Create minimal no_std application. See [smallest no_std](https://docs.rust-embedded.org/embedonomicon/smallest-no-std.html) for example. 
    <details>
    <summary>Code</summary>

    ```
    #![no_main]
    #![no_std]
    #![feature(lang_items)]

    use core::panic::PanicInfo;

    #[panic_handler]
    fn panic(_panic: &PanicInfo<'_>) -> ! {
        loop {}
    }

    #[lang = "eh_personality"]
    extern "C" fn eh_personality() {}
    ```

    <details>
2.  Create custom target specification based on built-in x86_64-unknown-none:
    ```
    rustc -Z unstable-options --print target-spec-json --target x86_64-unknown-none > x86_64-custom.json
    sed -i 's/"is-builtin": true/"is-builtin": false/' x86_64-custom.json
    ```
3. `cargo build --target x86_64-custom.json  -Zbuild-std=core`
4. Change `"panic-behaviour": "abort"` to `"panic-behaviour": "unwind"` in `x86_64-custom.json`
5. `cargo build --target x86_64-custom.json  -Zbuild-std=core` will fail

Note: I have a minimal [repository](https://github.com/iliakonnov/rust-crash/tree/unstable-fingerprints) with all these steps done

### Meta
```
rustc 1.59.0-nightly (83b15bfe1 2021-12-28)
binary: rustc
commit-hash: 83b15bfe1c15f325bc186ebfe3691b729ed59f2b
commit-date: 2021-12-28
host: x86_64-unknown-linux-gnu
release: 1.59.0-nightly
LLVM version: 13.0.0
```

### Error output
I've omitted part of error since it is enormous. Full log available [here](https://github.com/iliakonnov/rust-crash/blob/f1310de97542a3494a4f85565931edb661e0a87d/error.log).

```
error: internal compiler error: encountered incremental compilation error with exported_symbols(core[32cd])
  |
  = help: This is a known issue with the compiler. Run `cargo clean -p minimal` or `cargo clean` to allow your project to compile
  = note: Please follow the instructions below to create a bug report with the provided information
  = note: See <https://github.com/rust-lang/rust/issues/84970> for more information

thread 'rustc' panicked at 'Found unstable fingerprints for exported_symbols(core[32cd]): [ …omitted… ]', compiler/rustc_query_system/src/query/plumbing.rs:675:9
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/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md
note: rustc 1.59.0-nightly (83b15bfe1 2021-12-28) running on x86_64-unknown-linux-gnu
note: compiler flags: -Z unstable-options -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type bin
note: some of the compiler flags provided by cargo are hidden

query stack during panic:
#0 [exported_symbols] exported_symbols
end of query stack
error: could not compile `minimal` due to previous error

Caused by:
  process didn't exit successfully: `rustc --crate-name minimal --edition=2018 src/main.rs --error-format=json --json=diagnostic-rendered-ansi,future-incompat --crate-type bin --emit=dep-info,link -C embed-bitcode=no -C debuginfo=2 -C metadata=17370ef95f3ae4d6 -C extra-filename=-17370ef95f3ae4d6 --out-dir /home/ilia/Documents/asos/minimal/target/x86_64-custom/debug/deps --target /home/ilia/Documents/asos/minimal/x86_64-custom.json -C incremental=/home/ilia/Documents/asos/minimal/target/x86_64-custom/debug/incremental -L dependency=/home/ilia/Documents/asos/minimal/target/x86_64-custom/debug/deps -L dependency=/home/ilia/Documents/asos/minimal/target/debug/deps --extern 'noprelude:compiler_builtins=/home/ilia/Documents/asos/minimal/target/x86_64-custom/debug/deps/libcompiler_builtins-253f3d368d5adfbe.rlib' --extern 'noprelude:core=/home/ilia/Documents/asos/minimal/target/x86_64-custom/debug/deps/libcore-3e5d30ea51ef9363.rlib' -Z unstable-options` (exit status: 101)
```


<details><summary><strong>Backtrace</strong></summary>
<p>

```
stack backtrace:
   0: rust_begin_unwind
             at /rustc/83b15bfe1c15f325bc186ebfe3691b729ed59f2b/library/std/src/panicking.rs:498:5
   1: core::panicking::panic_fmt
             at /rustc/83b15bfe1c15f325bc186ebfe3691b729ed59f2b/library/core/src/panicking.rs:107:14
   2: rustc_query_system::query::plumbing::incremental_verify_ich_cold
   3: rustc_query_system::query::plumbing::incremental_verify_ich::<rustc_query_impl::plumbing::QueryCtxt, rustc_span::def_id::CrateNum, &[(rustc_middle::middle::exported_symbols::ExportedSymbol, rustc_middle::middle::exported_symbols::SymbolExportLevel)]>
   4: rustc_query_system::query::plumbing::try_load_from_disk_and_cache_in_memory::<rustc_query_impl::plumbing::QueryCtxt, rustc_span::def_id::CrateNum, &[(rustc_middle::middle::exported_symbols::ExportedSymbol, rustc_middle::middle::exported_symbols::SymbolExportLevel)]>
   5: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_span::def_id::CrateNum, &[(rustc_middle::middle::exported_symbols::ExportedSymbol, rustc_middle::middle::exported_symbols::SymbolExportLevel)]>>
   6: rustc_query_system::query::plumbing::get_query::<rustc_query_impl::queries::exported_symbols, rustc_query_impl::plumbing::QueryCtxt>
   7: rustc_codegen_ssa::back::linker::exported_symbols
   8: <core::iter::adapters::map::Map<core::slice::iter::Iter<rustc_session::config::CrateType>, <rustc_codegen_ssa::CrateInfo>::new::{closure#0}> as core::iter::traits::iterator::Iterator>::fold::<(), core::iter::traits::iterator::Iterator::for_each::call<(rustc_session::config::CrateType, alloc::vec::Vec<alloc::string::String>), <hashbrown::map::HashMap<rustc_session::config::CrateType, alloc::vec::Vec<alloc::string::String>, core::hash::BuildHasherDefault<rustc_hash::FxHasher>> as core::iter::traits::collect::Extend<(rustc_session::config::CrateType, alloc::vec::Vec<alloc::string::String>)>>::extend<core::iter::adapters::map::Map<core::slice::iter::Iter<rustc_session::config::CrateType>, <rustc_codegen_ssa::CrateInfo>::new::{closure#0}>>::{closure#0}>::{closure#0}>
   9: <rustc_codegen_ssa::CrateInfo>::new
  10: rustc_codegen_ssa::back::write::start_async_codegen::<rustc_codegen_llvm::LlvmCodegenBackend>
  11: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
  12: <rustc_session::session::Session>::time::<alloc::boxed::Box<dyn core::any::Any>, rustc_interface::passes::start_codegen::{closure#0}>
  13: <rustc_interface::queries::Queries>::ongoing_codegen
  14: <rustc_interface::interface::Compiler>::enter::<rustc_driver::run_compiler::{closure#1}::{closure#2}, core::result::Result<core::option::Option<rustc_interface::queries::Linker>, rustc_errors::ErrorReported>>
  15: rustc_span::with_source_map::<core::result::Result<(), rustc_errors::ErrorReported>, rustc_interface::interface::create_compiler_and_run<core::result::Result<(), rustc_errors::ErrorReported>, rustc_driver::run_compiler::{closure#1}>::{closure#1}>
  16: rustc_interface::interface::create_compiler_and_run::<core::result::Result<(), rustc_errors::ErrorReported>, rustc_driver::run_compiler::{closure#1}>
  17: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_interface::util::setup_callbacks_and_run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_errors::ErrorReported>, rustc_driver::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_errors::ErrorReported>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_errors::ErrorReported>>
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
```

</p>
</details>

This requires nightly since it uses `-Zbuild-std=core` which is not stable
@rustbot requires-nightly A-incr-comp

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Found unstable fingerprints for exported_symbols with custom target #92403

iliakonnov
openedon Dec 29, 2021

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