[clang] [clang-repl] Handle frontend options for clang-repl before calling executeAction (PR #132670)

[Anutosh Bhat via cfe-commits]

anutosh491 wrote:

Hey @serge-sans-paille 

Sorry for missing your last reply completely. Thanks for going through it in the first place :)

I've added a small test to get us started 

https://github.com/llvm/llvm-project/pull/132670/files#diff-339061dce5c23e378165cd07b0511a10e5f921803cb8d7ac76a220cdb3eb54a8

We would get the following as a whole
```
(base) anutosh491 at Anutoshs-MacBook-Air bin % ./clang-repl --Xcc -Xclang --Xcc -version                                      
LLVM (http://llvm.org/):
  LLVM version 21.0.0git
  Optimized build.
clang-repl: Version displayed
```
But I am just checking the presence of the string "Version displayed" cause the version number and the output through help is subject to change in the future.


https://github.com/llvm/llvm-project/pull/132670