[clang] [clang-repl] fix error recovery while parsing completely fails (PR #127087)

[Anutosh Bhat via cfe-commits]

anutosh491 wrote:

There are quite some made by @kr-2003 and me here.

1) We realize even without this fix, stuff worked perfectly on our Macos ARM devices. So looks like a Ubuntu issue anyways

![image](https://github.com/user-attachments/assets/666d5cc4-1f42-4c4a-8ff6-81aa67bc4650)

2) Obviously the try-catch block works when wrapped inside a class/function (not a top level decl)

3) If we build clang-repl with different configs, it works 

i) `-DCMAKE_BUILD_TYPE=RelWithDebInfo -DLLVM_ENABLE_PROJECTS=clang -DLLVM_USE_SPLIT_DWARF=ON -DLLVM_USE_LINKER=lld`

With this 
```
(base) abhinav at jarvis-2223:~/Desktop/Coding/llvm-project/build/bin$ ./clang-repl --version
LLVM (http://llvm.org/):
  LLVM version 20.1.0-rc1
  Optimized build.
(base) abhinav at jarvis-2223:~/Desktop/Coding/llvm-project/build/bin$ ./clang-repl
clang-repl> #include <iostream>
clang-repl> try { throw 1; } catch { std::cout << "Caught Exception" << std::endl; }
In file included from <<< inputs >>>:1:
input_line_2:1:23: error: expected '('
    1 | try { throw 1; } catch { std::cout << "Caught Exception" << std::endl; }
      |                       ^
      |                       (
error: Parsing failed.
clang-repl>
```

ii) With the following it fails.

```
-DLLVM_ENABLE_PROJECTS=clang                        \
        -DLLVM_TARGETS_TO_BUILD="host;NVPTX"                \
        -DCMAKE_BUILD_TYPE=Release                          \
        -DLLVM_ENABLE_ASSERTIONS=ON                         \
        -DCLANG_ENABLE_STATIC_ANALYZER=OFF                  \
        -DCLANG_ENABLE_ARCMT=OFF                            \
        -DCLANG_ENABLE_FORMAT=OFF                           \
        -DCLANG_ENABLE_BOOTSTRAP=OFF                        \
        -DLLVM_ENABLE_ZSTD=OFF                              \
        -DLLVM_ENABLE_TERMINFO=OFF                          \
        -DLLVM_ENABLE_LIBXML2=OFF                           \
        
```

Abhinav, could you also past the diff between how using two different configs affects the build ?
Maybe that might point us to the root cause behind all of this.

https://github.com/llvm/llvm-project/pull/127087