cc_test: emit errors if there's duplicate in srcs

In general "srcs" property allows duplication in the list.
But when cc_test's "test_per_src" property is set "true",
there will be variants according to "srcs" list.
Therefore, it should fail if there is a duplicate entry
in srcs list.

Bug: 113629474
Test: mma
Change-Id: I543624459c30dd296494a3a80e28ce5503a3ea2f