[clang] [clang-repl] Fix the process return code if diagnostics occurred. (PR #89879)

[Stefan Gränitz via cfe-commits]

weliveindetail wrote:

> The Unix pre-merge seems okay, however the windows pre-merge check is doing nothing for more than 12h.

Yeah same here. I recognized that Windows PR checks are running Flang regression tests now. I guess that adds a huge load on the builders and causes the delays. Mine was cancelled after 15h.. https://github.com/llvm/llvm-project/pull/89734

@philnik777 Brought it up in Discord on Wednesday https://discord.com/channels/636084430946959380/645949235295944724/1232232568196173846

https://github.com/llvm/llvm-project/pull/89879