Convert googletest and nanopb CMake builds to add_subdirectory (#1522)

* Add a download-only boringssl ExternalProject

Match boringssl version to grpc submodule version

Note: not yet in use

* Split grpc into separate download and build tasks

This allows other external targets to download into the gRPC source tree
before grpc is actually built.

* Convert grpc to an http download

* Build googletest with add_subdirectory

Also:
  * Revert library-name modifications in the abseil-cpp build
  * Move abseil-cpp add_subdirectory build into place

* Build nanopb with add_subdirectory

* Force nanopb first to work around ODR violations

This is a temporary work-around for b/111328563.

0 files changed, 0 insertions, 0 deletions