[clang] [clang-repl] Extend the C support. (PR #89804)

[Vassil Vassilev via cfe-commits]

vgvassilev wrote:

Ok, maybe I can you test this patch for a temporary fix until we figure out what's going wrong.
```diff
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 7f6921ea22be..d771a060f305 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -2285,7 +2285,7 @@ void Sema::ActOnPopScope(SourceLocation Loc, Scope *S) {
     // Partial translation units that are created in incremental processing must
     // not clean up the IdResolver because PTUs should take into account the
     // declarations that came from previous PTUs.
-    if (!PP.isIncrementalProcessingEnabled())
+    if (!PP.isIncrementalProcessingEnabled() && !getLangOpts().IncrementalExtensions)
       IdResolver.RemoveDecl(D);
 
     // Warn on it if we are shadowing a declaration.
```

https://github.com/llvm/llvm-project/pull/89804