Correct the way that libelf is linked when USDT is used.
The default for UDPLITE_RECV_CSCOV is zero. RFC 3828 recommend
that this means full checksum coverage for received packets.
If an application is willing to accept packets with partial
coverage, it is expected to use the socekt option and provice
the minimum coverage it accepts.

Reviewed by: kevlo
MFC after: 3 days
Consistently cast tty and user to const char * in printf()-like contexts.
Set default cycle state in case of early interrupts.

MFC after:	3 days
Remove MK_ARM_EABI, the armeb issues have been fixed. The code to support
the oabi is still in the tree, but it is expected this will be removed
as developers work on surrounding code.

With this commit the ARM EABI is the only supported supported ABI by
FreeBSD on ARMa 32-bit processors.

X-MFC after:	never
Relnotes:	yes
Differential Revision: https://reviews.freebsd.org/D876