A fresh checkout of native_client lacks some components that Subzero's "make -f Makefile.standalone presubmit" needs.

Add explicit checks for these components, and when missing, print suggestions for how to create them.

BUG= https://bugs.chromium.org/p/nativeclient/issues/detail?id=4359
R=jpp@chromium.org, smklein@chromium.org

Review URL: https://codereview.chromium.org/1782343003 .