[flang] [clang] [llvm] [AArch64][Driver] Better handling of target feature dependencies (PR #78270)

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@@ -308,6 +312,94 @@ inline constexpr ExtensionInfo Extensions[] = {
 };
 // clang-format on
 
+struct ExtensionSet {
+  // Set of extensions which are currently enabled.
+  ExtensionBitset Enabled;
+  // Set of extensions which have been enabled or disabled at any point. Used
+  // to avoid cluttering the cc1 command-line with lots of unneeded features.
+  ExtensionBitset Touched;
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ostannard wrote:

Yes, that's correct.

https://github.com/llvm/llvm-project/pull/78270