Android.rules: build with "unified android headers"
Android.rules: build with "unified android headers"

Unified headers will be the only way to build applications in NDK r16,
and it also works with NDK r15.

This also bumps the minimum supported android version to 16.

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@316985 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,llvm-mirror/lldb