[Object] Allow iterating over an IRObjectFile's modules
[Object] Allow iterating over an IRObjectFile's modules

If you've already loaded an IRObjectFile and need access to the
Modules themselves you shouldn't have to reparse a byte stream to do
it. Adds an accessor for the modules in IRObjectFile.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@335759 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm