Merge "Revert "libprocessgroup: Remove __BEGIN_DECLS and __END_DECLS"" into main am: 5c14720b5a

Original change: https://android-review.googlesource.com/c/platform/system/core/+/3366140

Change-Id: I37a8597906ebb918bf8f82408aab2a4e2e1e9a50
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>