emulator: Add libqemu static library to implement qemu pipes.

See hardware/libhardware/include/hardware/qemu_pipe.h for the API
implemented by the library. It enables very fast reads/writes between
the guest system and specific emulator services.

Define BUILD_LIBQEMU_TESTS=true in your environment to build the
test programs (a simple host ping-pong server, and a benchmark
guest program).

You can invoke them with:

1/ Testing TCP pipes:

   host:  test-libqemu-1 -tcp 8012
   guest: test-libqemu-2 -pipe tcp:8012

Alternatively

   guest: su
          test-libqemu-2 -tcp 8012

2/ Testing Unix pipes:

   host:  test-libqemu-1 -unix /tmp/libqemu-socket
   guest: test-libqemu-2 -pipe unix:/tmp/libqemu-socket

3/ Testing internal pingpong server (within the emulator)

   host:   /* nothing to do */
   guest:  test-libqemu-2

Change-Id: Ib50fc9cbee6b5f4581baca97412d6f69d4f84860
9 files changed