[clang] [clang] Fix options handling in ClangExtDefMapGen.cpp (PR #176116)

[Davide Cunial via cfe-commits]

capitan-davide wrote:

> I think this deserves a test case. Could you add a LIT test?

Sure, https://github.com/llvm/llvm-project/pull/176116/commits/67cdfd9245959a346dc3be34527f4e35f8b70a3c

https://github.com/llvm/llvm-project/pull/176116