translate / export weak lang items

see rust-lang#51671 for details

fixes rust-lang#51671
fixes rust-lang#51342

Author: japaric

src/librustc/middle/weak_lang_items.rs

@@ -17,6 +17,7 @@ use rustc_target::spec::PanicStrategy;
 use syntax::ast;
 use syntax::symbol::Symbol;
 use syntax_pos::Span;
+use hir::def_id::DefId;
 use hir::intravisit::{Visitor, NestedVisitorMap};
 use hir::intravisit;
 use hir;
@@ -145,6 +146,15 @@ impl<'a, 'tcx, 'v> Visitor<'v> for Context<'a, 'tcx> {
     }
 }
 
+impl<'a, 'tcx, 'gcx> TyCtxt<'a, 'tcx, 'gcx> {
+    pub fn is_weak_lang_item(&self, item_def_id: DefId) -> bool {
+        let lang_items = self.lang_items();
+        let did = Some(item_def_id);
+
+        $(lang_items.$name() == did)||+
+    }
+}
+
 ) }
 
 weak_lang_items! {

src/librustc_mir/monomorphize/collector.rs

@@ -1031,6 +1031,7 @@ impl<'b, 'a, 'v> RootCollector<'b, 'a, 'v> {
             MonoItemCollectionMode::Lazy => {
                 self.entry_fn == Some(def_id) ||
                 self.tcx.is_reachable_non_generic(def_id) ||
+                self.tcx.is_weak_lang_item(def_id) ||
                 self.tcx.codegen_fn_attrs(def_id).flags.contains(
                     CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
             }

src/test/run-make-fulldeps/issue-51671/Makefile

@@ -0,0 +1,13 @@
+-include ../tools.mk
+
+ifdef IS_WINDOWS
+# Do nothing on MSVC.
+all:
+	exit 0
+else
+all:
+	$(RUSTC) --emit=obj app.rs
+	nm $(TMPDIR)/app.o | $(CGREP) rust_begin_unwind
+	nm $(TMPDIR)/app.o | $(CGREP) rust_eh_personality
+	nm $(TMPDIR)/app.o | $(CGREP) rust_oom
+endif

src/test/run-make-fulldeps/issue-51671/app.rs

@@ -0,0 +1,18 @@
+#![crate_type = "bin"]
+#![feature(lang_items)]
+#![feature(panic_implementation)]
+#![no_main]
+#![no_std]
+
+use core::panic::PanicInfo;
+
+#[panic_implementation]
+fn panic(_: &PanicInfo) -> ! {
+    loop {}
+}
+
+#[lang = "eh_personality"]
+fn eh() {}
+
+#[lang = "oom"]
+fn oom() {}