[Polly] Move SimplifyVisitor into polly namespace.

Declarations in headers should not be in the anonymous
namespace. Compilers also warn about the use of
<anon namespace>::SimplifyVisitor as a public field in
polly::SimplifyPass and polly::SimplifyPrinterPass.
GitOrigin-RevId: fc115f2e73a2049211efa231b6c54c29248efdf5
2 files changed