Add option to build with stable

  error: internal compiler error: src/librustc/hir/def.rs:385: attempted .def_id() on invalid res: Err

  thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:892:9
  stack backtrace:
     0:     0x7fd3894065d4 - backtrace::backtrace::libunwind::trace::hc586f95f659e6084
                                 at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/libunwind.rs:88
     1:     0x7fd3894065d4 - backtrace::backtrace::trace_unsynchronized::ha9827fdb593fd967
                                 at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/mod.rs:66
     2:     0x7fd3894065d4 - std::sys_common::backtrace::_print_fmt::h00c888c95e07165a
                                 at src/libstd/sys_common/backtrace.rs:84
     3:     0x7fd3894065d4 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h8407ffb2d059bc74
                                 at src/libstd/sys_common/backtrace.rs:61
     4:     0x7fd38943ecec - core::fmt::write::h4165a12a3856465f
                                 at src/libcore/fmt/mod.rs:1024
     5:     0x7fd3893fa937 - std::io::Write::write_fmt::h499a0566ceaa0048
                                 at src/libstd/io/mod.rs:1428
     6:     0x7fd38940aa7e - std::sys_common::backtrace::_print::h05fbb11587298e2b
                                 at src/libstd/sys_common/backtrace.rs:65
     7:     0x7fd38940aa7e - std::sys_common::backtrace::print::h8021a3ed2b5ff07e
                                 at src/libstd/sys_common/backtrace.rs:50
     8:     0x7fd38940aa7e - std::panicking::default_hook::{{closure}}::hd3a6326f5c6c149f
                                 at src/libstd/panicking.rs:193
     9:     0x7fd38940a771 - std::panicking::default_hook::h7088fb00a0cb1faf
                                 at src/libstd/panicking.rs:210
    10:     0x7fd3734d3248 - <alloc::boxed::Box<F> as core::ops::function::Fn<A>>::call::ha9a0e3c625716847
                                 at /rustc/fdc0011561c6365c596dfd8fa1ef388162bc89c7/src/liballoc/boxed.rs:983
    11:     0x7fd3734d7a84 - proc_macro::bridge::client::<impl proc_macro::bridge::Bridge>::enter::{{closure}}::{{closure}}::hd6bd7ccb0bdaefed
                                 at /rustc/fdc0011561c6365c596dfd8fa1ef388162bc89c7/src/libproc_macro/bridge/client.rs:305
    12:     0x7fd38940b230 - std::panicking::rust_panic_with_hook::h6b223bff7721d4c1
                                 at src/libstd/panicking.rs:475
    13:     0x7fd38ba6256d - std::panicking::begin_panic::h8ef26d2aea648f22
    14:     0x7fd38ba969a0 - rustc_errors::HandlerInner::bug::h6b233e840067cebc
    15:     0x7fd38ba9568a - rustc_errors::Handler::bug::hb654993c1e76b21a
    16:     0x7fd38b36df9b - rustc::util::bug::opt_span_bug_fmt::{{closure}}::h056cc1cdf743dd12
    17:     0x7fd38b36ca33 - rustc::ty::context::tls::with_opt::{{closure}}::he8758b5e67be4aee
    18:     0x7fd38b36c9eb - rustc::ty::context::tls::with_opt::h944a0b8dbaa86ba6
    19:     0x7fd38b36dea8 - rustc::util::bug::opt_span_bug_fmt::hae9ab10c0feecbc5
    20:     0x7fd38b36de12 - rustc::util::bug::bug_fmt::h886f94e8d4bb0f0b
    21:     0x556d8c032ee2 - rustc::hir::def::Res<Id>::def_id::{{closure}}::h635d7f9433dcef5e
    22:     0x556d8c06edf2 - rustdoc::clean::register_res::h48d433549701437b
    23:     0x556d8c1503ee - <syntax_pos::source_map::Spanned<rustc::hir::VisibilityKind> as rustdoc::clean::Clean<rustdoc::clean::Visibility>>::clean::h49051be75d01b5e8
    24:     0x556d8c11e6e4 - <rustc::hir::StructField as rustdoc::clean::Clean<rustdoc::clean::Item>>::clean::h5e93a91f40d130ad
    25:     0x556d8c1c6900 - <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter::h50cc920a3f15ad93
    26:     0x556d8c11edb4 - <rustdoc::doctree::Struct as rustdoc::clean::Clean<rustdoc::clean::Item>>::clean::h3304943530443092
    27:     0x556d8c115fb1 - <rustdoc::doctree::Module as rustdoc::clean::Clean<rustdoc::clean::Item>>::clean::h18c1955c1f582d3f
    28:     0x556d8c116331 - <rustdoc::doctree::Module as rustdoc::clean::Clean<rustdoc::clean::Item>>::clean::h18c1955c1f582d3f
    29:     0x556d8c116331 - <rustdoc::doctree::Module as rustdoc::clean::Clean<rustdoc::clean::Item>>::clean::h18c1955c1f582d3f
    30:     0x556d8c116331 - <rustdoc::doctree::Module as rustdoc::clean::Clean<rustdoc::clean::Item>>::clean::h18c1955c1f582d3f
    31:     0x556d8c066609 - rustdoc::clean::krate::h500052b81e82211b
    32:     0x556d8c0d9c8f - rustc::ty::context::tls::enter_global::hb6e5b84eb752cea9
    33:     0x556d8c0ae1b3 - rustc_interface::interface::run_compiler_in_existing_thread_pool::h7a4bf6c65cd2ef69
    34:     0x556d8c28c748 - std::panicking::try::do_call::had10e69eb7c0fd8f
    35:     0x7fd38941bd0a - __rust_maybe_catch_panic
                                 at src/libpanic_unwind/lib.rs:78
    36:     0x556d8c2883be - rustc_driver::catch_fatal_errors::h9519cfc4ab58ee18
    37:     0x556d8c0465ba - rustdoc::main_options::h6fa48593da911d49
    38:     0x556d8c25c8b4 - std::thread::local::LocalKey<T>::with::hc2830240e0119ac9
    39:     0x556d8c12f4ce - scoped_tls::ScopedKey<T>::set::h8b122eaf66ecd628
    40:     0x556d8c2a0984 - syntax::with_globals::h5410313cd41d17b9
    41:     0x556d8c0aea72 - std::sys_common::backtrace::__rust_begin_short_backtrace::he357e176bbab3f66
    42:     0x7fd38941bd0a - __rust_maybe_catch_panic
                                 at src/libpanic_unwind/lib.rs:78
    43:     0x556d8c133ee9 - core::ops::function::FnOnce::call_once{{vtable.shim}}::h21e3347670049c74
    44:     0x7fd3893ec88f - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::h9ef9eb6ec2ee6be0
                                 at /rustc/fdc0011561c6365c596dfd8fa1ef388162bc89c7/src/liballoc/boxed.rs:969
    45:     0x7fd38941a730 - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::hc0fc46e9a64f076e
                                 at /rustc/fdc0011561c6365c596dfd8fa1ef388162bc89c7/src/liballoc/boxed.rs:969
    46:     0x7fd38941a730 - std::sys_common::thread::start_thread::h4eee21a391e25c99
                                 at src/libstd/sys_common/thread.rs:13
    47:     0x7fd38941a730 - std::sys::unix::thread::Thread::new::thread_start::h673f7c20aae94594
                                 at src/libstd/sys/unix/thread.rs:80
    48:     0x7fd3891876db - start_thread
    49:     0x7fd388c9888f - __clone
    50:                0x0 - <unknown>
  error: aborting due to previous error

  error: Could not document `abi_stable`.

  Caused by:
    process didn't exit successfully: `rustdoc --edition=2018 --crate-type lib --crate-name abi_stable abi_stable/src/lib.rs -o '[redacted]/abi_stable_crates/target/doc' --cfg 'feature="channels"' --cfg 'feature="crossbeam-channel"' --cfg 'feature="default"' --cfg 'feature="serde_json"' --error-format=json --json=diagnostic-rendered-ansi -L 'dependency=[redacted]/abi_stable_crates/target/debug/deps' --extern 'abi_stable_derive=[redacted]/abi_stable_crates/target/debug/deps/libabi_stable_derive-dff63361c452ddd1.so' --extern 'abi_stable_shared=[redacted]/abi_stable_crates/target/debug/deps/libabi_stable_shared-a014f0489f9ded5a.rmeta' --extern 'core_extensions=[redacted]/abi_stable_crates/target/debug/deps/libcore_extensions-e62cb7643589c738.rmeta' --extern 'crossbeam_channel=[redacted]/abi_stable_crates/target/debug/deps/libcrossbeam_channel-24cdc3968a67dddd.rmeta' --extern 'generational_arena=[redacted]/abi_stable_crates/target/debug/deps/libgenerational_arena-9d2bda75b8618542.rmeta' --extern 'libloading=[redacted]/abi_stable_crates/target/debug/deps/liblibloading-8e22a41a3a91c5e8.rmeta' --extern 'lock_api=[redacted]/abi_stable_crates/target/debug/deps/liblock_api-6a62490fb191d43f.rmeta' --extern 'parking_lot=[redacted]/abi_stable_crates/target/debug/deps/libparking_lot-cad3989fbf66bad1.rmeta' --extern 'serde=[redacted]/abi_stable_crates/target/debug/deps/libserde-65fb8b5741d2fe57.rmeta' --extern 'serde_derive=[redacted]/abi_stable_crates/target/debug/deps/libserde_derive-86d96a74bd7eff56.so' --extern 'serde_json=[redacted]/abi_stable_crates/target/debug/deps/libserde_json-8969eba699194ab2.rmeta' --cfg 'feature="rust_1_36"' --cfg 'feature="rust_1_38"' --cfg 'feature="rust_1_39"' --cfg 'feature="nightly_rust"'` (exit code: 1)