fixup! [REBASEME] rustc_target: move comment to macro

Author: tamird

compiler/rustc_target/src/lib.rs

@@ -140,9 +140,9 @@ macro_rules! target_spec_enum {
             /// an enum. However, it is possible to have arbitrary values in a
             /// target JSON file (which can be parsed when `--target` is
             /// specified). This might occur, for example, for an out-of-tree
-            /// codegen backend that supports a value that rustc currently
-            /// doesn't know about. This variant exists as an escape hatch for
-            /// such cases.
+            /// codegen backend that supports a value (e.g. architecture or OS)
+            /// that rustc currently doesn't know about. This variant exists as
+            /// an escape hatch for such cases.
             $( #[$other_variant_attr] )*
             $OtherVariant(crate::spec::StaticCow<str>),
         }