Add support for target aliases

Author: kulikjak

compiler/rustc_session/src/config.rs

@@ -1433,7 +1433,7 @@ fn parse_target_triple(matches: &getopts::Matches, error_format: ErrorOutputType
                 early_error(error_format, &format!("target file {:?} does not exist", path))
             })
         }
-        Some(target) => TargetTriple::TargetTriple(target),
+        Some(target) => TargetTriple::from_alias(target),
         _ => TargetTriple::from_triple(host_triple()),
     }
 }

compiler/rustc_target/src/spec/mod.rs

@@ -1800,6 +1800,24 @@ impl TargetTriple {
         Ok(TargetTriple::TargetPath(canonicalized_path))
     }
 
+    /// Creates a target triple from its alias
+    pub fn from_alias(triple: String) -> Self {
+        macro_rules! target_aliases {
+            ( $(($alias:literal, $target:literal ),)+ ) => {
+                match triple.as_str() {
+                    $( $alias => TargetTriple::from_triple($target), )+
+                    _ => TargetTriple::TargetTriple(triple),
+                }
+            }
+        }
+
+        target_aliases! {
+            // `x86_64-pc-solaris` is an alias for `x86_64_sun_solaris` for backwards compatibility reasons.
+            // (See <https://github.com./rust-lang/rust/issues/40531>.)
+            ("x86_64-pc-solaris", "x86_64-sun-solaris"),
+        }
+    }
+
     /// Returns a string triple for this target.
     ///
     /// If this target is a path, the file name (without extension) is returned.