[clang] [AIX][clang][driver] fix no-pthread option (PR #69363)

[Hubert Tong via cfe-commits]

hubert-reinterpretcast wrote:

@daltenty, can we also have a check that the driver does not pass `-pthread` to the frontend when `-no-pthread` is used?

As a complication, I think the code responsible is common cross-platform code in [clang/Driver/ToolChains/Clang.cpp](https://github.com/llvm/llvm-project/blob/df3478e480b3b2e9fe125697b7931dc48b09e450/clang/lib/Driver/ToolChains/Clang.cpp#L6537).

To exacerbate things, the ineffectiveness of `-no-pthread` in terms of the linker invocation occurs on multiple other platforms (and I am not sure that fixing just the frontend invocation leaves us in a better state for those platforms).

https://github.com/llvm/llvm-project/pull/69363