[Polly] Disable vectorization for Polly's fallback loops (#119188)

The patch sets the vectorization metadata to false for Polly's fallback
loops. These are the loops executed when RTCs fail. This minimizes the
multiple loop versioning carried out by Polly and subsequently by the
Loop Vectorizer.

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Co-authored-by: Michael Kruse <github@meinersbur.de>
GitOrigin-RevId: 4b3a878e8a24c13f8dc435e91304d8692d8cb42b
20 files changed