Bianca van Schaik authored 4 years ago and Brad King committed 4 years ago

Starting with Clang 12, `otool -l` reports `LC_LOAD_WEAK_DYLIB` instead
of `LC_LOAD_DYLIB` for weakly linked libraries.  Update the
implementation of `file(GET_RUNTIME_DEPENDENCIES)` to recognize these.

Fixes: #21684