[clang] [Multilib] Custom flags YAML parsing (PR #110657)

[Simon Tatham via cfe-commits]

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@@ -101,6 +101,25 @@ class Multilib {
 
 raw_ostream &operator<<(raw_ostream &OS, const Multilib &M);
 
+namespace custom_flag {
+struct CustomFlagDeclaration;
+using CustomFlagDeclarationPtr = std::shared_ptr<CustomFlagDeclaration>;
+
+struct CustomFlagValueDetail {
+  std::string Name;
+  std::optional<SmallVector<std::string>> ExtraBuildArgs;
+  CustomFlagDeclarationPtr Decl;
+};
+
+struct CustomFlagDeclaration {
+  std::string Name;
+  SmallVector<CustomFlagValueDetail> ValueList;
+  size_t DefaultValueIdx = ~0UL;
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statham-arm wrote:

Perhaps this would be clearer as an `optional<size_t>`?

https://github.com/llvm/llvm-project/pull/110657