[clang-repl] Fix error recovery while PTU cleanup (llvm#127467)

Fixes llvm#123300

What is seen 
```
clang-repl> int x = 42;
clang-repl> auto capture = [&]() { return x * 2; };
In file included from <<< inputs >>>:1:
input_line_4:1:17: error: non-local lambda expression cannot have a capture-default
    1 | auto capture = [&]() { return x * 2; };
      |                 ^
zsh: segmentation fault  clang-repl --Xcc="-v"

(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x8)
  * frame #0: 0x0000000107b4f8b8 libclang-cpp.19.1.dylib`clang::IncrementalParser::CleanUpPTU(clang::PartialTranslationUnit&) + 988
    frame #1: 0x0000000107b4f1b4 libclang-cpp.19.1.dylib`clang::IncrementalParser::ParseOrWrapTopLevelDecl() + 416
    frame #2: 0x0000000107b4fb94 libclang-cpp.19.1.dylib`clang::IncrementalParser::Parse(llvm::StringRef) + 612
    frame llvm#3: 0x0000000107b52fec libclang-cpp.19.1.dylib`clang::Interpreter::ParseAndExecute(llvm::StringRef, clang::Value*) + 180
    frame llvm#4: 0x0000000100003498 clang-repl`main + 3560
    frame llvm#5: 0x000000018d39a0e0 dyld`start + 2360
```

Though the error is justified, we shouldn't be interested in exiting
through a segfault in such cases.

The issue is that empty named decls weren't being taken care of
resulting into this assert


https://github.com/llvm/llvm-project/blob/c1a229252617ed58f943bf3f4698bd8204ee0f04/clang/include/clang/AST/DeclarationName.h#L503

Can also be seen when the example is attempted through xeus-cpp-lite.


![image](https://github.com/user-attachments/assets/9b0e6ead-138e-4b06-9ad9-fcb9f8d5bf6e)

Author: anutosh491

clang/lib/Interpreter/IncrementalParser.cpp

@@ -176,7 +176,7 @@ void IncrementalParser::CleanUpPTU(TranslationUnitDecl *MostRecentTU) {
   // FIXME: We should de-allocate MostRecentTU
   for (Decl *D : MostRecentTU->decls()) {
     auto *ND = dyn_cast<NamedDecl>(D);
-    if (!ND)
+    if (!ND || ND->getDeclName().isEmpty())
       continue;
     // Check if we need to clean up the IdResolver chain.
     if (ND->getDeclName().getFETokenInfo() && !D->getLangOpts().ObjC &&

clang/test/Interpreter/lambda.cpp

@@ -1,7 +1,8 @@
 // REQUIRES: host-supports-jit
 // UNSUPPORTED: system-aix
 // RUN: cat %s | clang-repl | FileCheck %s
-// RUN: cat %s | clang-repl -Xcc -O2 | FileCheck %s
+// RUN: cat %s | clang-repl -Xcc -Xclang -Xcc -verify -Xcc -O2 | FileCheck %s
+
 extern "C" int printf(const char *, ...);
 
 auto l1 = []() { printf("ONE\n"); return 42; };
@@ -14,4 +15,14 @@ auto r2 = l2();
 auto r3 = l2();
 // CHECK: TWO
 
-%quit
+// Verify non-local lambda capture error is correctly reported
+int x = 42;
+
+// expected-error {{non-local lambda expression cannot have a capture-default}}
+auto capture = [&]() { return x * 2; };
+
+// Ensure interpreter continues and x is still valid
+printf("x = %d\n", x);
+// CHECK: x = 42
+
+%quit