cmd/buildlet: add aix-ppc64 to list of targets in Makefile
cmd/buildlet: add aix-ppc64 to list of targets in Makefile

Change-Id: Ic9a50a9850f59911ad78f98170b3534b16d13302
Reviewed-on: https://go-review.googlesource.com/c/build/+/168437
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/build,golang/build,golang/build,golang/build