In the fallout from the OpenSSL heartbleed bug, OpenBSD developers forked OpenSSL into LibreSSL. Initially the only supported platform for LibreSSL was OpenBSD, but the BSD developers are pushing harder now for platform portability.

OpenBSD developers added reallocarray.c as a single, easily-included file for anyone who wants to include it to make LibreSSL run on their platform.

More details on the LibreSSL portability improvement can be found at Undeadly.org.