Update the Swift version numbers reported by objdump

Summary:
Add Swift 4.1, Swift 4.2, and Swift 5 version numbers to objdump's
MachODump's print_imae_info routines. 

rdar://46548425

Reviewers: pete, lhames, bob.wilson

Reviewed By: pete, bob.wilson

Subscribers: bob.wilson, llvm-commits

Differential Revision: https://reviews.llvm.org/D55442

llvm-svn: 348632