* Migrate most of our tests to use `split-file` instead of `echo`
* Remove individual `rm -f %t/libfoo.a` commands in favor of a top-level `rm -rf %t`
* Remove unused `Inputs/libfunction.s`
Reviewed By: #lld-macho, compnerd
Differential Revision: https://reviews.llvm.org/D93604
Handle the case where there are both common and non-common definitions
of the same symbol. Add a bunch of tests to ensure compatibility with ld64.
Reviewed By: #lld-macho, gkm
Differential Revision: https://reviews.llvm.org/D86910