[clang-tools-extra] [clang-cl] Fix value of __FUNCTION__ in MSVC mode. (PR #67592)

[Aaron Ballman via cfe-commits]

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@@ -291,6 +291,10 @@ struct PrintingPolicy {
   /// parameters.
   unsigned AlwaysIncludeTypeForTemplateArgument : 1;
 
+  // Prints "class" keyword before type template arguments. This is used when
+  // printing a function via the _FUNCTION__ or __func__ macro in MSVC mode.
+  unsigned UseClassForTemplateArgument : 1;
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AaronBallman wrote:

This comment really threw me off because I thought this was about `template <typename Ty>` vs `template <class Ty>` and it's actually about whether we print an elaborated type specifier or not.

It would be nice if we could reuse `SuppressElaboration` for this purpose instead of adding a new policy field for it, but do we not have an `ElaboratedType` for the template argument and so we would never try to print the elaboration. So we really need the opposite, which is `ForcePrintingAsElaboratedType` (or similar) as a more general type printing feature. So that code like `S` will force writing `struct S` or `class S` even though an elaborated type was not used in source. WDYT?

https://github.com/llvm/llvm-project/pull/67592