[llvm] [Support] Add clang tooling generated explicit visibility macros (PR #113097)

[Saleem Abdulrasool via llvm-commits]

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@@ -157,7 +157,7 @@ class ErrorInfoBase {
 /// *All* Error instances must be checked before destruction, even if
 /// they're moved-assigned or constructed from Success values that have already
 /// been checked. This enforces checking through all levels of the call stack.
-class [[nodiscard]] Error {
+class LLVM_ABI [[nodiscard]] Error {
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compnerd wrote:

@AaronBallman - I don't remember off hand what the correct order is for attributes and extension attributes. Should this be `[[nodiscard]] __declspec(...)` or `__declspec(...) [[nodiscard]]`?

https://github.com/llvm/llvm-project/pull/113097