[clang] [clang-repl] Lay the basic infrastructure for pretty printing of types (PR #148701)

[Aaron Ballman via cfe-commits]

================
@@ -300,16 +640,17 @@ llvm::Expected<Expr *> Interpreter::ExtractValueFromExpr(Expr *E) {
 using namespace clang;
 
 // Temporary rvalue struct that need special care.
-REPL_EXTERNAL_VISIBILITY void *
+REPL_EXTERNAL_VISIBILITY extern "C" void *
----------------
AaronBallman wrote:

IIRC, I think this should be:
```
extern "C" void * REPL_EXTERNAL_VISIBILITY func();
```
CC @compnerd 

https://github.com/llvm/llvm-project/pull/148701