Add dirgroup for trusty genrule am: 44b6f30e10

Original change: https://android-review.googlesource.com/c/platform/external/libcxx/+/3304097

Change-Id: If0c194cf3d616c8458b27f7a42ea06a220bc5d3a
Signed-off-by: Automerger Merge Worker <[email protected]>