[Tint] Fix source loc for builtin attributes

This info was accidentally dropped in:
https://dawn-review.googlesource.com/c/dawn/+/197775

Bug: 353716474
Change-Id: I799d69198fbebba8c61185e971e96342a4a6dc14
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/199175
Commit-Queue: Natalie Chouinard <chouinard@google.com>
Reviewed-by: James Price <jrprice@google.com>
diff --git a/src/tint/lang/wgsl/reader/parser/parser.cc b/src/tint/lang/wgsl/reader/parser/parser.cc
index 2abc56e..4a5660a 100644
--- a/src/tint/lang/wgsl/reader/parser/parser.cc
+++ b/src/tint/lang/wgsl/reader/parser/parser.cc
@@ -3050,7 +3050,7 @@
                 }
                 match(Token::Type::kComma);
 
-                return builder_.Builtin(name.value);
+                return builder_.Builtin(t.source(), name.value);
             });
     }