Print a warning if `llvm-libtool-darwin` if any of the object
files provided by the user have the same file name.
The tool will now print a warning if there is a name collision across:
* Two object files
* An object file and an object file from within a static library
* Two object files from different static libraries
Here is an example of the error:
```
$ llvm-libtool-darwin -static -o archive.a out.o out.o
error: file 'out.o' was specified multiple times.
in: out.o
in: out.o
$ llvm-libtool-darwin -static -o archive.a out.o
$ llvm-libtool-darwin -static -o combined.a archive.a out.o
error: file 'out.o' was specified multiple times.
in: archive.a
in: out.o
```
This change mimics apple's cctools libtool's behavior which always shows a warning in such cases.
Reviewed By: smeenai
Differential Revision: https://reviews.llvm.org/D113130
Add support for passing in libraries via `-l` and `-L` options to
`llvm-libtool-darwin`.
Reviewed by jhenderson, smeenai
Differential Revision: https://reviews.llvm.org/D85540
Shoaib Meenai