As of a recent change, test_support always included the headers, which
causes Android's new build-system to be unhappy. It doesn't want to
include headers. Split them into test_support_headers and test_support
to match the other keys.

Then fix up references:

- Android's new build system only wants the sources. Fix this.

- Chromium's GN and GYP theoretically want the sources and headers, but
  we've never supplied the headers because this isn't enforced at all.
  Fix this. Headers are selected based on what target the header
  "belongs to".

- Bazel has no change except to sort test_support_sources.

Change-Id: I85809e70a71236b5e91d87f87bb73bc2ea289251
Reviewed-on: https://boringssl-review.googlesource.com/9044
Reviewed-by: Adam Langley <agl@google.com>