[clang] Objective C: use C++ exceptions on MinGW+GNUstep (PR #77255)

[Frederik Carlier via cfe-commits]

qmfrederik wrote:

@compnerd @davidchisnall I've addressed the feedback and CI is (mostly) green.  The build failure on Windows seems unrelated:


```
# Removing c:/ws\src
# Creating "c:/ws\src"
> git clone -v -- https://github.com/llvm-premerge-tests/llvm-project.git .
Cloning into '.'...
remote: Internal Server Error
fatal: unable to access 'https://github.com/llvm-premerge-tests/llvm-project.git/': The requested URL returned error: 500
```



https://github.com/llvm/llvm-project/pull/77255