Add a parameter to getCopyToParts and getCopyFromParts to specify whether

Add a parameter to getCopyToParts and getCopyFromParts to specify whether
endian swapping should be done, and update the code to use it. This fixes
some register ordering issues on big-endian systems, such as PowerPC,
introduced by the recent illegal by-val arguments changes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@37921 91177308-0d34-0410-b5e6-96231b3b80d8