ICE when static global allocator is defined in main function

[WildCryptoFox]

While writing some doctests for a custom allocator this popped up. Easy fix for the doc test, just add # fn main() {} after the static.

playground

fn main() {
    #[global_allocator]
    static A: usize = 0;
}

Compiling playground v0.0.1 (/playground)
error[E0432]: unresolved import `super::A`
 --> src/main.rs:3:5
  |
3 |     static A: usize = 0;
  |     ^^^^^^^^^^^^^^^^^^^^ no `A` in the root

thread 'rustc' panicked at 'assertion failed: prev.is_none()', src/librustc/middle/region.rs:442:13
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
   1: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:70
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:58
             at src/libstd/panicking.rs:200
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:215
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:482
   6: std::panicking::begin_panic
   7: <rustc::middle::region::RegionResolutionVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_stmt
   8: <rustc::middle::region::RegionResolutionVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_block
   9: rustc::middle::region::resolve_expr
  10: <rustc::middle::region::RegionResolutionVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_body
  11: rustc::middle::region::region_scope_tree
  12: rustc::ty::query::__query_compute::region_scope_tree
  13: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::region_scope_tree<'tcx>>::compute
  14: rustc::dep_graph::graph::DepGraph::with_task_impl
  15: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_get_with
  16: rustc_typeck::check::regionck::<impl rustc_typeck::check::FnCtxt<'a, 'gcx, 'tcx>>::regionck_item
  17: rustc::ty::context::GlobalCtxt::enter_local
  18: rustc_typeck::check::wfcheck::check_item_well_formed
  19: rustc::ty::query::__query_compute::check_item_well_formed
  20: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::check_item_well_formed<'tcx>>::compute
  21: rustc::dep_graph::graph::DepGraph::with_task_impl
  22: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_get_with
  23: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::ensure_query
  24: rustc::hir::Crate::visit_all_item_likes
  25: rustc::util::common::time
  26: rustc_typeck::check_crate
  27: <std::thread::local::LocalKey<T>>::with
  28: rustc::ty::context::TyCtxt::create_and_enter
  29: rustc_driver::driver::compile_input
  30: rustc_driver::run_compiler_with_pool
  31: <scoped_tls::ScopedKey<T>>::set
  32: rustc_driver::run_compiler
  33: <scoped_tls::ScopedKey<T>>::set
query stack during panic:
#0 [region_scope_tree] processing `main`
#1 [check_item_well_formed] processing `main`
end of query stack
error: aborting due to previous error

For more information about this error, try `rustc --explain E0432`.

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-nightly (852701ad6 2019-02-01) running on x86_64-unknown-linux-gnu

note: compiler flags: -C codegen-units=1 -C debuginfo=2 --crate-type bin

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

error: Could not compile `playground`.

To learn more, run the command again with --verbose.

[petrochenkov]

Fixed in #62735.