detect ARM Linux EABI OSARCH as linux-gnu instead of linux-gnueabi

* Set OSARCH to linux-gnu even if host_os is linux-gnueabi
* When checking if we are Linux, check OSARCH rather than host_os

The newer ARM ABI ("EABI") shows the OS name 'linux-gnueabi' rather than
'linux-gnu' . This patch sets OSARCH to be 'linux-gnu' even in such a case.

OSARCH is tested for the value of 'linux-gnu' in one or two places in the
tree. This patch also fixes the check libcap to check for $OSARCH rather
than $host_os .

See also: http://wiki.debian.org/ArmEabiPort

Merged revisions 225957 via svnmerge from 
http://svn.digium.com/svn/asterisk/branches/1.4


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@226018 65c4cc65-6c06-0410-ace0-fbb531ad65f3