[clang][cli] Parse & generate options necessary for LangOptions defaults manually

It turns out we need to handle `LangOptions` separately from the rest of the options. `LangOptions` used to be conditionally parsed only when `!(DashX.getFormat() == InputKind::Precompiled || DashX.getLanguage() == Language::LLVM_IR)` and we need to restore this order (for more info, see D94682).

D94682 moves the parsing of marshalled `LangOpts` from `parseSimpleArgs` back to `ParseLangArgs`.

We need to parse marshalled `LangOpts` **after** `ParseLangArgs` calls `setLangDefaults`. This will enable future patches, where values of some `LangOpts` depend on the defaults.

However, two language options (`-finclude-default-header` and `-fdeclare-opencl-builtins`) need to be parsed **before** `ParseLangArgs` calls `setLangDefaults`, because they are necessary for setting up OpenCL defaults correctly.
This patch implements this by removing their marshalling info and manually parsing (and generating) them exactly where necessary.

Reviewed By: Bigcheese

Differential Revision: https://reviews.llvm.org/D94678