Merging r314898:

Merging r314898:
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r314898 | dylanmckay | 2017-10-04 23:37:22 +1300 (Wed, 04 Oct 2017) | 6 lines

[AVR] Implement LPMWRdZ pseudo-instruction's expansion.

FIXME: implementation is mostly copy-pasted from LDWRdPtr, so we should
refactor a bit and unify the two

Patch by Gerdo Erdi.
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_50@315836 91177308-0d34-0410-b5e6-96231b3b80d8