gccrs: attributes: Handle external tool annotations like rustfmt::

gcc/rust/ChangeLog:

	* util/rust-attribute-values.h: Add RUSTFMT value.
	* util/rust-attributes.cc: Define the attribute.
	* util/rust-attributes.h (enum CompilerPass): Add EXTERNAL variant.
	* expand/rust-macro-builtins.cc: Fix formatting.

gcc/rust/expand/rust-macro-builtins.cc

@@ -83,7 +83,6 @@ const BiMap<std::string, BuiltinMacro> MacroBuiltin::builtins = {{
   {"Ord", BuiltinMacro::Ord},
   {"PartialOrd", BuiltinMacro::PartialOrd},
   {"Hash", BuiltinMacro::Hash},
-
 }};
 
 AST::MacroTranscriberFunc

gcc/rust/util/rust-attribute-values.h

@@ -83,6 +83,8 @@ public:
   static constexpr auto &FUNDAMENTAL = "fundamental";
 
   static constexpr auto &NON_EXHAUSTIVE = "non_exhaustive";
+
+  static constexpr auto &RUSTFMT = "rustfmt";
 };
 } // namespace Values
 } // namespace Rust

gcc/rust/util/rust-attributes.cc

@@ -94,7 +94,8 @@ static const BuiltinAttrDefinition __definitions[]
      {Attrs::RUSTC_ON_UNIMPLEMENTED, STATIC_ANALYSIS},
 
      {Attrs::FUNDAMENTAL, TYPE_CHECK},
-     {Attrs::NON_EXHAUSTIVE, TYPE_CHECK}};
+     {Attrs::NON_EXHAUSTIVE, TYPE_CHECK},
+     {Attrs::RUSTFMT, EXTERNAL}};
 
 BuiltinAttributeMappings *
 BuiltinAttributeMappings::get ()

gcc/rust/util/rust-attributes.h

@@ -40,7 +40,10 @@ enum CompilerPass
   HIR_LOWERING,
   TYPE_CHECK,
   STATIC_ANALYSIS,
-  CODE_GENERATION
+  CODE_GENERATION,
+
+  // External Rust tooling attributes, like #[rustfmt::skip]
+  EXTERNAL,
 
   // Do we need to add something here for const fns?
 };