Enable CMake builds within AOSP with build_cmake.rs
- Some build dependency crates like `pkg-config` and `cmake` are not in
AOSP, so this prevents projects with only AOSP crates to build grpcio
- In Cargo.toml, make the dependency crates not in AOSP as optional
- Create build_cmake.rs for build script to link with prebuilt gRPC
library by an environment variable GRPCIO_SYS_GRPC_INCLUDE_PATH
Test: tools/external_updater/updater.sh update --refresh --keep-date --keep-local-changes --no-upload external/rust/crates/grpcio-sys
Test: TH
Change-Id: I99d0badd248628779c49d86a209c415c380d5f4a
5 files changed
