MFC r212286:

MFC r212286:

GCC defines built-ins for atomic instructions found on i486 and higher.
Because FreeBSD no longer supports the 80386 cpu all code targeting
FreeBSD/i386 necessarily runs on i486 or higher so the compiler
built-ins can be used by default inside libstdc++ and in C++ headers.
This allows newly compiled C++ code to inline some atomic operations.
Old binaries continue to use libstdc++ functions.

PR:		148926
Tested by:	Yuri Karaban <tech askold net>
Approved by:	kib (mentor)

git-svn-id: svn://svn.freebsd.org/base/stable/8@212962 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f