[lldb] Teach LocateExecutableSymbolFile to look into LOCALBASE on FreeBSD (#81355)

FreeBSD ports will now install debuginfo under $LOCALBASE/lib/debug/, where $LOCALBASE is typically /usr/local. On FreeBSD search this path in addition to existing debug info paths.

Relevant change on the FreeBSD side: https://reviews.freebsd.org/D43515