https://boringssl-review.googlesource.com/c/boringssl/+/31364 wants to
add a dependency to each target, which is much easier with fewer of
them. Start with decrepit.

Change-Id: Ib3777063d545dfebe3e2b8448eb7e5bbb5c3aaac
Reviewed-on: https://boringssl-review.googlesource.com/31584
Reviewed-by: Adam Langley <agl@google.com>