Build amazon-ssm-agent directly from the port Makefile rather than recursing
into the makefile distributed with the source code. In particular, this
should fix the build on i386, where it is currently broken due to amd64
being hard-coded as the build architecture. Numerous other cleanups to the
build. [1]

Change LICENSE and remove subsidiary variables, as Amazon has relicensed
this from the "Amazon" license to Apache 2.0.

Submitted by: swills [1]