[Driver] Don't preprocess source files when reproducing linker crashes

It's not necessary to redo the source file preprocessing for reproducing linker
crashes because we must have successfully created the object file by this point.
Skip this step, and also don't report the preprocessed source file or create
the clang invocation shell script. The latter is no longer sensible without the
preprocessed source, or helpful given the linker reproducer will have it's own
shell script.

Differential Revision: https://reviews.llvm.org/D137289