[llvm-rtdyld] Add support for passing command line arguments to rtdyld-run code.

The --args option can now be used to pass arguments to code linked with
llvm-rtdyld. E.g.

$ llvm-rtdyld file1.o file2.o --args a b c

is equivalent to:

$ ld -o program file1.o file2.o
$ ./program a b c

This is the rtdyld counterpart to the jitlink change in r359115, and makes
benchmarking and comparison between the tools easier.

llvm-svn: 359168