[Legalizer] Add support for G_OR NarrowScalar.

[Legalizer] Add support for G_OR NarrowScalar.

Legalize bitwise OR:
 A = BinOp<Ty> B, C
into:
 B1, ..., BN = G_UNMERGE_VALUES B
 C1, ..., CN = G_UNMERGE_VALUES C
 A1 = BinOp<Ty/N> B1, C2
 ...
 AN = BinOp<Ty/N> BN, CN
 A = G_MERGE_VALUES A1, ..., AN

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@314760 91177308-0d34-0410-b5e6-96231b3b80d8