[llvm] [TableGen] New tblgen Pattern bit to disable DAG pattern imports during GISel (PR #88382)

[via llvm-commits]

================
@@ -4378,7 +4378,8 @@ void CodeGenDAGPatterns::ParsePatterns() {
       FindPatternInputsAndOutputs(Pattern, Pattern.getTree(j), InstInputs,
                                   InstResults, InstImpResults);
 
-    ParseOnePattern(CurPattern, Pattern, Result, InstImpResults);
+    ParseOnePattern(CurPattern, Pattern, Result, InstImpResults,
----------------
jofrn wrote:

Moving the check here allows us to use `GISelShouldIgnore` in any TG backend that might use it (so at least both `-gen-dag-isel` and `-gen-global-isel`), so it'd be appropriate to rename the bit to `ISelShouldIgnore`, as it can be used to also disable DAGISel Pattern records in particular.

Since it could be used for any backend though, we can name it PatternShouldIgnore or just ShouldIgnore (since it is already on a Pattern).

https://github.com/llvm/llvm-project/pull/88382