libbinder: RPC flake mode fix

The #ifdef should be #if because RPC_FLAKE_PRONE is defined to false.
[[clang::no_destroy]] is needed for the static variables in
rpcMaybeWaitToFlake otherwise it can crash for taking a mutex that was
destroyed in the onLastStrongRef->sendDecStrong path.

Test: atest binderRpcTest
Fixes: 190828148
Change-Id: Iac6302d737de70f5fde2656dd2e140a6dcd13f7e