Adding `static_ndk_lib: true` to a module installs the static library
to the NDK sysroot.
Test: Set property for libc.a, make ndk
Test: Set property for libc.a, scripts/build-ndk-prebuilts.sh
Bug: https://github.com/android-ndk/ndk/issues/272
Change-Id: Ib368a25705f2adb7129dac207c1b727d4ccc1eb2