[X86] When lowering uniform shifts, use X86ISD::VZEXT instead of using a ZERO_EXTEND_VECTOR_INREG. If we emit the ZERO_EXTEND_VECTOR_INREG too late it doesn't get lowered properly and makes it through to isel and fails.
[X86] When lowering uniform shifts, use X86ISD::VZEXT instead of using a ZERO_EXTEND_VECTOR_INREG. If we emit the ZERO_EXTEND_VECTOR_INREG too late it doesn't get lowered properly and makes it through to isel and fails.

Fixes PR31593.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@291535 91177308-0d34-0410-b5e6-96231b3b80d8

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