commit 1d409987bb369b88e1af344a7c83ea4ec4354607
author Primiano Tucci <primiano@google.com> Thu Sep 19 10:15:18 2019 +0100
committer Primiano Tucci <primiano@google.com> Thu Sep 19 10:15:18 2019 +0100
tree fb42e882625bba7abc97059fdfaa20a0dcc6a45f
parent edf199a0b96c320b90fbbbc285f5587d6317a8df

tools/gen_bazel: Standalone Bazel build

Updates the gen_bazel generator and generates
a BUILD file that allows to build traced, traced_probes
perfetto and trace_processor both on Linux and Mac.
This also allows easy integration with google internal builds.
The major differences of the new generator are:
1. Uses the new way of dealing with protobuf libraries
   (proto_library -> cc_proto_library -> executable target
   see go/new-proto-library)
2. Instead of repeating all the source files in each target
   it creates Bazel filegroup(s) out of GN source_set(s).
   While doing so it takes care of propagating up flags and
   dependencies. This is because Bazel filegroup(s),
   conversely to GN source_set(s), are pure bags of sources.

Still missing:
 - cflags / ldflags propagation into Bazel.
 - Android toolchain (perhaps will never happen)

This will require a matching change to Google internal
sources.

Test: bazel build //:all
Change-Id: Ic1c725bd83e2a5e92eebb5c5b34728cf6d5983e6