[clang] [clang][ssaf] Fix building on gcc-7 and MinGW/Cygwin (PR #181812)

[Balázs Benics via cfe-commits]

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@@ -42,4 +44,9 @@ class MockSerializationFormat final : public SerializationFormat {
 
 } // namespace clang::ssaf
 
+namespace llvm {
+extern template class CLANG_TEMPLATE_ABI
+    Registry<clang::ssaf::MockSerializationFormat::FormatInfo>;
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steakhal wrote:

Most definitely. I'm frequently looking at unit tests to see how certain APIs should be used in a minimal context. This should set the example. I'll also come back to document how to add new registries for ssaf, so that we wouldn't trigger this build error again.
If only we had a way to side step this statically at compile time using clang,...

https://github.com/llvm/llvm-project/pull/181812