Add malloc test support to unit tests.

Currently far from passing and I haven't even tried with a leak checker yet.
Also bn_test is slow.

Change-Id: I4fe2783aa5f7897839ca846062ae7e4a367d2469
Reviewed-on: https://boringssl-review.googlesource.com/4794
Reviewed-by: Adam Langley <agl@google.com>
26 files changed