[clang][deps] NFC: Refactor inferred modules test

This patch squashes two tests with identical inputs into a single test, and adopts the `split-file` utility. This allows us to remove `sed` invocation with multiple commands, where "s|-E|-x objective-c -E|g" could've caused issues if previous replacements injected path containing "-E".

Reviewed By: benlangmuir

Differential Revision: https://reviews.llvm.org/D143615