MFC r273381 (by bapt):

MFC r273381 (by bapt):

Add support for __cxa_throw_bad_array_new_length in libcxxrt

It is required for use with newer g++49

Differential Revision:	https://reviews.freebsd.org/D982
Reviewed by:	theraven
Approved by:	theraven

MFC r276417:

Import libcxxrt master 00bc29eb6513624824a6d7db2ebc768a4216a604.

Interesting fixes:
76584a0  Reorganize code to use only 32bit atomic ops for 32bit platforms
30d2ae5  Implement __cxa_throw_bad_array_new_length

Reviewed by:	bapt
Differential Revision: https://reviews.freebsd.org/D1390

git-svn-id: svn://svn.freebsd.org/base/stable/10@278017 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f