[clang] [Clang] Rework LTO mode selection to be a Toolchain property (PR #201155)

[Matt Arsenault via cfe-commits]

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@@ -462,6 +464,17 @@ class ToolChain {
   /// native LLVM support.
   virtual bool HasNativeLLVMSupport() const;
 
+  /// Returns the default LTO mode for this toolchain.
+  virtual LTOKind getDefaultLTOMode() const;
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arsenm wrote:

I think those are all terrible too 

https://github.com/llvm/llvm-project/pull/201155