[automerger skipped] Add a soong var that will be used to enable/disabe rust...

[automerger skipped] Add a soong var that will be used to enable/disabe rust relevant targets am: 5b7787ec am: 5e6a2f7e am: b6b731d1 -s ours am: 643f20a8 -s ours

am skip reason: skip tag Change-Id I21945b25e3e4e04e6110030d45b82fa1acf6c409 with SHA-1 09132f63 is already in history

Original change: https://android-review.googlesource.com/c/platform/packages/modules/DnsResolver/+/1642562

Change-Id: Id89e1a293ab611749aa9c5becbee4c58ccca43fa