Build a different mksnapshot for each arch.

Since mksnapshot uses different source files for each
arch, building it in a single location fails when switching
between builds.

This uses a separate version for each arch, using the
same variable that is used to select which source files
get built.

Change-Id: I8608bf3b0f85571c75c7f6b21e47091ef8ed8c3f
2 files changed