Import a new libcxxrt.  This fixes some potential crashing in the demangler.

Approved by:	re (gjb)
MFC after:	1 week
Fix DELAY() on RPi, the wrong math was making it take twice it should.

Reported by:	Alexander <sht@ropnet.ru>
Approved by:	adrian (mentor)
Approved by:	re (gjb)