Remove SharedEmitterMessage::AbortIfErrors.

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

Author: nnethercote

Diff for: 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);
                 }