re PR libgcj/3694 (natPlainDatagramSocketImpl.cc doesn't compile in ALPHA OSF1)

re PR libgcj/3694 (natPlainDatagramSocketImpl.cc doesn't compile in ALPHA OSF1)

	* include/posix.h (_POSIX_PII_SOCKET): Define.
	* configure.in (HAVE_SOCKLEN_T): Define.
	* java/net/natPlainSocketImpl.cc [!HAVE_SOCKLEN_T]: Move socklen_t
	definition up.
	(_JV_accept): New function, avoids Tru64 UNIX accept macro.
	(java::net::PlainSocketImpl::accept): Use it.
	Fixes PRs libgcj/3694, libgcj/3696.

	* configure.in (HAVE_STRUCT_IPV6_MREQ): New test.
	* acconfig.h (HAVE_STRUCT_IPV6_MREQ): Provide template.
	* configure, include/config.h.in: Regenerate.
	* java/net/natPlainDatagramSocketImpl.cc (union McastReq): Use it.
	(mcastGrp): Likewise.
	(java::net::PlainDatagramSocketImpl::setOption): Guard against
	missing IPV6_MULTICAST_IF.
	Fixes PR libgcj/3694.

From-SVN: r44546