Introduced CHECK-START-{x,y,z} syntax.

Rationale:
Many of our tests repeat CHECK-START-x with following
checker lines for various architectures if some, but
not all architectures match the checker lines. This
is tedious and error-prone. No more of that nonsense!
This CL introduces a syntax that allows specifying
subsets of architectures with a single block!

Bug: 62352954

Test: test-art-host test-art-target
Change-Id: Ife18b3ef9eaa2540166ace045c165ba252b31c6b