[clang] [LIT] Add -nostdinc so system headers aren't searched with implicit module maps (PR #192125)

[Qiongsi Wu via cfe-commits]

qiongsiwu wrote:

Thanks @perry-ca for the PR! Could you help me understand why are we only modifying these specific tests for zOS? There are many other dependency scanning tests not modified. Are the remaining tests affected as well? 

https://github.com/llvm/llvm-project/pull/192125