Enable use of libpffft in system-side unit tests am: a16a548b69 am: 516d50cef3 am: 3ed4f11f79

Original change: https://android-review.googlesource.com/c/platform/external/pffft/+/2281089

Change-Id: I09249345c3e74d732618eacb07ed953cb97752b9
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>