When support for --separate-debug was added (https://github.com/mongodb/mongo/commit/6d475fdb5a76acab760ce4b6709b60a4c8c9aec6) as part of mobile development, we intended to strip local symbols, where doing so was appropriate and perhaps important for size reasons.
Later, we started using --separate-debug for all builds, whether or not stripping local symbols was appropriate.
As a result, macOS builds are having local symbol information stripped, which may result in inferior debugging or backtracing. We should remove the -x flag from the $STRIP invocation on Darwin in separate_debug.py.