[JITLink] Add support for passing arguments to jit-linked code.

[JITLink] Add support for passing arguments to jit-linked code.

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

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

is equivalent to:

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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@359115 91177308-0d34-0410-b5e6-96231b3b80d8