LTO: Use a common LibLTOCodeGenerator::init, NFC
LTO: Use a common LibLTOCodeGenerator::init, NFC

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@266538 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 9c9a101118f43fe813359dbbce3ff5bc35b370d0)

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