[clang][cli] NFC: Add PIE parsing for precompiled input and IR

This patch effectively reverts a small part of D83979.

When we stop parsing `LangOpts` unconditionally in `parseSimpleArgs` (above the diff) and move them back to `ParseLangArgs` (called in `else` branch) in D94682, `LangOpts.PIE` would never get parsed in this `if` branch. This patch ensures this doesn't happen.

Right now, this causes `LangOpts.PIE` to be parsed twice, but that will be immediately corrected in D94682.

Reviewed By: Bigcheese

Differential Revision: https://reviews.llvm.org/D94679