GlobalISel: partially revert r308540.
GlobalISel: partially revert r308540.

An unfinished and untested implementation of ISel for G_UNMERGE_VALUES crept in
by mistake.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@308542 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit f54b9c71c77bde497fce22277cad0f82c626962c)

apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm