Avoid parsing const unsafe/extern functions as async

gcc/rust/ChangeLog:

	* parse/rust-parse-impl.h
	(Parser::parse_vis_item):
	Call parse_function instead of parse_async_item when finding
	UNSAFE or EXTERN_KW during lookahead.

gcc/testsuite/ChangeLog:

	* rust/compile/func-const-unsafe.rs: New test.

Signed-off-by: Owen Avery <powerboat9.gamer@gmail.com>

Author: powerboat9

gcc/rust/parse/rust-parse-impl.h

@@ -1382,10 +1382,10 @@ Parser<ManagedTokenSource>::parse_vis_item (AST::AttrVec outer_attrs)
 	case IDENTIFIER:
 	case UNDERSCORE:
 	  return parse_const_item (std::move (vis), std::move (outer_attrs));
-	case UNSAFE:
-	case EXTERN_KW:
 	case ASYNC:
 	  return parse_async_item (std::move (vis), std::move (outer_attrs));
+	case UNSAFE:
+	case EXTERN_KW:
 	case FN_KW:
 	  return parse_function (std::move (vis), std::move (outer_attrs));
 	default:

gcc/testsuite/rust/compile/func-const-unsafe.rs

@@ -0,0 +1 @@
+pub const unsafe fn foo() {}