Mark incremental-ignore-spans as TRACKED.

Using that options basically changes all stable hashes we may compute.
Adding/removing as UNTRACKED it makes everything ICE (unstable fingerprint
everywhere).  As TRACKED, it can still do its job without ICEing.

Author: cjgillot

compiler/rustc_interface/src/tests.rs

@@ -652,7 +652,6 @@ fn test_unstable_options_tracking_hash() {
     untracked!(future_incompat_test, true);
     untracked!(hir_stats, true);
     untracked!(identify_regions, true);
-    untracked!(incremental_ignore_spans, true);
     untracked!(incremental_info, true);
     untracked!(incremental_verify_ich, true);
     untracked!(input_stats, true);
@@ -737,6 +736,7 @@ fn test_unstable_options_tracking_hash() {
     tracked!(fuel, Some(("abc".to_string(), 99)));
     tracked!(function_sections, Some(false));
     tracked!(human_readable_cgu_names, true);
+    tracked!(incremental_ignore_spans, true);
     tracked!(inline_in_all_cgus, Some(true));
     tracked!(inline_mir, Some(true));
     tracked!(inline_mir_hint_threshold, Some(123));

compiler/rustc_session/src/options.rs

@@ -1333,7 +1333,7 @@ options! {
         "generate human-readable, predictable names for codegen units (default: no)"),
     identify_regions: bool = (false, parse_bool, [UNTRACKED],
         "display unnamed regions as `'<id>`, using a non-ident unique id (default: no)"),
-    incremental_ignore_spans: bool = (false, parse_bool, [UNTRACKED],
+    incremental_ignore_spans: bool = (false, parse_bool, [TRACKED],
         "ignore spans during ICH computation -- used for testing (default: no)"),
     incremental_info: bool = (false, parse_bool, [UNTRACKED],
         "print high-level information about incremental reuse (or the lack thereof) \