Rewrite llvm-lto's codegen() using ThinCodeGenerator::run(). NFC-ish.
Rewrite llvm-lto's codegen() using ThinCodeGenerator::run(). NFC-ish.

Differential Revision: https://reviews.llvm.org/D33360

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@303437 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 3770b2b84847bfdb5dc99ff90a4d3c4c33291bb1)

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