[clang] [libcxx] [libc++] Re-enable the clang_modules_include test for Objective-C++ (PR #66801)

[Mark de Wever via cfe-commits]

mordante wrote:

> I tried to fix this in [c2c840b](https://github.com/llvm/llvm-project/commit/c2c840bd92cfac155f6205ff7505b109b301d389). Sorry for disturbing.

Thanks for the quick fix! I've tested the fix with this patch locally and it passes.

https://github.com/llvm/llvm-project/pull/66801