[X86] Add scalar shl+lshr -> shift+mask tests (PR40758)
[X86] Add scalar shl+lshr -> shift+mask tests (PR40758)

As discussed on D61068, many x86 targets can perform 2 immediate shifts quicker than a shift + mask

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@360530 91177308-0d34-0410-b5e6-96231b3b80d8

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