Declare py_exec_tools_toolchain. am: 976a380312

Original change: https://android-review.googlesource.com/c/platform/prebuilts/build-tools/+/3403189

Change-Id: Ib8defea852e02f868a692346a0ac3c1f385644e5
Signed-off-by: Automerger Merge Worker <[email protected]>