syntax: Fix span on illegal ABI errors

Fixes #8537
Fixes #14499

src/libsyntax/parse/parser.rs

@@ -4537,7 +4537,7 @@ fn parse_opt_abi(&mut self) -> Option<abi::Abi> {
                     Some(abi) => Some(abi),
                     None => {
                         self.span_err(
-                            self.span,
+                            self.last_span,
                             format!("illegal ABI: expected one of [{}], \
                                      found `{}`",
                                     abi::all_names().connect(", "),

src/test/compile-fail/issue-8537.rs

+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+pub extern
+  "invalid-abi" //~ ERROR illegal ABI
+fn foo() {}
+
+fn main() {}