In -fsyntax-only mode we don't have llvm::Module.
Fix iterators.

Two things first the iterator wasn't considered to be empty.
Second the loop written such assumes chances to the collection
within the loop which is not the case.
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Add support for C tentative definitions.
Allow the unloading even in -fsyntax-only mode.
At least for verification purposes it is very useful.
In rawInput mode we want to be as close as possible to the compiler.
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