Adds a rust_defaults module that ensures that our crosvm modules are
only built on supported platforms.

Bug: 144553403
Bug: 140938178
Test: m -j crosvm.experimental
Test: modules disabled for unsupported platforms.
Change-Id: I0baec2b4f8c6839c858678270c1c6d527ba4716d

* Use a script cargo2android.py to generate Android.bp files
  from cargo build -v output. Cargo.toml and some build.rs
  files were temporarily changed to pass cargo build.
* Missing output are copied from old Android.bp file:
  * Rerun cargo2android.py in:
    ./tempfile ./gpu_display ./gpu_buffer ./gpu_renderer
  * Native code modules are not handled by cargo2android.py:
    * Copy modules from old Android.bp to ./gpu_display
    * Copy attributes of crosvm from old Android.bp to ./Android.bp
    * Copy libhost_cpuid to x86_64/Android.bp

Test: mm in crosvm and other rust directories.
Change-Id: I987dd881d088d950e073dc127d19240b6abc57f2

In Rust 2018 edition, `extern crate` is no longer required for importing
from other crates. Instead of writing:

    extern crate dep;
    use dep::Thing;

we write:

    use dep::Thing;

In this approach, macros are imported individually from the declaring
crate rather than through #[macro_use]. Before:

    #[macro_use]
    extern crate sys_util;

After:

    use sys_util::{debug, error};

The only place that `extern crate` continues to be required is in
importing the compiler's proc_macro API into a procedural macro crate.
This will hopefully be fixed in a future Rust release.

    extern crate proc_macro;

TEST=cargo check
TEST=cargo check --all-features
TEST=cargo check --target aarch64-unknown-linux-gnu
TEST=local kokoro

Change-Id: I0b43768c0d81f2a250b1959fb97ba35cbac56293
Reviewed-on: https://chromium-review.googlesource.com/1565302
Commit-Ready: David Tolnay <dtolnay@chromium.org>
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: David Tolnay <dtolnay@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: David Tolnay <dtolnay@chromium.org>

This matches the version already used by crostini_client.

The newer protobuf version depends on the tempfile crate rather than
tempdir, the latter being now deprecated. So I replaced our immitation
tempdir crate with one that matches the API of tempfile instead. As a
reminder, we use this crate as a patch to avoid pulling in all of the
rand crate and its many dependencies.

TEST=cargo check --features plugin
CQ-DEPEND=CL:1553971

Change-Id: I28eed3ceadb1013f015400b4c582aaf8dc89eee1
Reviewed-on: https://chromium-review.googlesource.com/1562924
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: David Tolnay <dtolnay@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Zach Reizner <zachr@chromium.org>
Reviewed-by: Daniel Verkamp <dverkamp@chromium.org>