Fix inconsistency in make-standalone-toolchain.sh

Fix to
1. abort when both --arch and --toolchain are specified but inconsistent
2. choose arm as advertized when none of --arch or --toolchain is specified
3. always echo when options are "auto-config"'d

BUG=21035291

Change-Id: I920e2dfa36ae7f4495d741a7eaa5143b45aa69a9
1 file changed