Remove SharedEmitterMessage::AbortIfErrors.

It's always paired wth `SharedEmitterMessage::Diagnostic`, so the two
can be merged.

compiler/rustc_codegen_ssa/src/back/write.rs

@@ -1783,7 +1783,6 @@ fn spawn_work<'a, B: ExtraBackendMethods>(
 enum SharedEmitterMessage {
  Diagnostic(Diagnostic),
  InlineAsmError(u32, String, Level, Option<(String, Vec<InnerSpan>)>),
- AbortIfErrors,
  Fatal(String),
 }
 
@@ -1852,7 +1851,6 @@ impl Emitter for SharedEmitter {
  args,
  })),
  );
- drop(self.sender.send(SharedEmitterMessage::AbortIfErrors));
  }
 
  fn source_map(&self) -> Option<&Lrc<SourceMap>> {
@@ -1894,6 +1892,7 @@ impl SharedEmitterMain {
  .collect();
  d.replace_args(diag.args);
  dcx.emit_diagnostic(d);
+ sess.dcx().abort_if_errors();
  }
  Ok(SharedEmitterMessage::InlineAsmError(cookie, msg, level, source)) => {
  assert!(matches!(level, Level::Error | Level::Warning | Level::Note));
@@ -1926,9 +1925,6 @@ impl SharedEmitterMain {
 
  err.emit();
  }
- Ok(SharedEmitterMessage::AbortIfErrors) => {
- sess.dcx().abort_if_errors();
- }
  Ok(SharedEmitterMessage::Fatal(msg)) => {
  sess.dcx().fatal(msg);
  }