[Clang][Driver] After default -fintegrated-cc1, make...

[Clang][Driver] After default -fintegrated-cc1, make llvm::report_fatal_error() generate preprocessed source + reproducer.sh again.

Added a test for #pragma clang __debug llvm_fatal_error to test for the original issue.
Added llvm::sys::Process::Exit() and replaced ::exit() in places where it was appropriate. This new function would call the current CrashRecoveryContext if one is running on the same thread; or call ::exit() otherwise.

Fixes PR44705.

Differential Revision: https://reviews.llvm.org/D73742