[CGP] add a reference to DataLayout in MemCmpExpansion; NFCI
[CGP] add a reference to DataLayout in MemCmpExpansion; NFCI

We're currently passing endian-ness around as a param (and not uniformly),
so this eliminates the need for that. I'd like to add a constant fold
call too, and that requires a DL.


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@305129 91177308-0d34-0410-b5e6-96231b3b80d8

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