[mach-o] Support -filelist option in darwin driver

The darwin linker has an option, heavily used by Xcode, in which, instead
of listing all input files on the command line, the input file paths are
written to a text file and the path of that text file is passed to the linker
with the -filelist option (similar to @file).

In order to make test cases for this, I generalized the -test_libresolution
option to become -test_file_usage.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@215762 91177308-0d34-0410-b5e6-96231b3b80d8