[clang] [clang][Dependency Scanning] Report Exported Modules during Scanning (PR #137421)

[Qiongsi Wu via cfe-commits]

qiongsiwu wrote:

Note to reviewers: 

`clang/test/ClangScanDeps/export.c` is the new test. The rest of the test changes are updates. 

https://github.com/llvm/llvm-project/pull/137421