Switch to FreeBSD for wcsstr and wmemcpy.

Almost all of our w* functions come from FreeBSD already. The one downside is
that we can't take all our w* functions from FreeBSD because FreeBSD handles
locales very differently from us.

Bug: N/A
Test: ran tests
Change-Id: I177b4332499992babd5d5afe5b3f469f8c4345a5