Mixed bazel/soong build prototype for genrule

With this change, bazel_module is a specifiable property on
genrule module definitions. With bazel-enabled mode, soong_build will
defer to Bazel for information on these modules.

source build/soong/bazelenv.sh to enter bazel-enabled mode.

Test: Manually verified on bionic/libc genrules using aosp_cf_x86_phone-userdebug
Change-Id: I3619848186d50be7273a5eba31c79989b981d408
diff --git a/bazel/bazelenv.sh b/bazel/bazelenv.sh
new file mode 100755
index 0000000..2ca8baf
--- /dev/null
+++ b/bazel/bazelenv.sh
@@ -0,0 +1,74 @@
+#!/bin/bash
+
+# Copyright 2020 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Helper script for setting environment variables required for Bazel/Soong
+# mixed builds prototype. For development use only.
+#
+# Usage:
+#   export BAZEL_PATH=[some_bazel_path] && source bazelenv.sh
+#
+# If BAZEL_PATH is not set, `which bazel` will be used
+# to locate the appropriate bazel to use.
+
+
+# Function to find top of the source tree (if $TOP isn't set) by walking up the
+# tree.
+function gettop
+{
+    local TOPFILE=build/soong/root.bp
+    if [ -n "${TOP-}" -a -f "${TOP-}/${TOPFILE}" ] ; then
+        # The following circumlocution ensures we remove symlinks from TOP.
+        (cd $TOP; PWD= /bin/pwd)
+    else
+        if [ -f $TOPFILE ] ; then
+            # The following circumlocution (repeated below as well) ensures
+            # that we record the true directory name and not one that is
+            # faked up with symlink names.
+            PWD= /bin/pwd
+        else
+            local HERE=$PWD
+            T=
+            while [ \( ! \( -f $TOPFILE \) \) -a \( $PWD != "/" \) ]; do
+                \cd ..
+                T=`PWD= /bin/pwd -P`
+            done
+            \cd $HERE
+            if [ -f "$T/$TOPFILE" ]; then
+                echo $T
+            fi
+        fi
+    fi
+}
+
+BASE_DIR="$(mktemp -d)"
+
+if [ -z "$BAZEL_PATH" ] ; then
+    export BAZEL_PATH="$(which bazel)"
+fi
+
+export USE_BAZEL=1
+export BAZEL_HOME="$BASE_DIR/bazelhome"
+export BAZEL_OUTPUT_BASE="$BASE_DIR/output"
+export BAZEL_WORKSPACE="$(gettop)"
+
+echo "USE_BAZEL=${USE_BAZEL}"
+echo "BAZEL_PATH=${BAZEL_PATH}"
+echo "BAZEL_HOME=${BAZEL_HOME}"
+echo "BAZEL_OUTPUT_BASE=${BAZEL_OUTPUT_BASE}"
+echo "BAZEL_WORKSPACE=${BAZEL_WORKSPACE}"
+
+mkdir -p $BAZEL_HOME
+mkdir -p $BAZEL_OUTPUT_BASE
diff --git a/bazel/master.WORKSPACE.bazel b/bazel/master.WORKSPACE.bazel
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/bazel/master.WORKSPACE.bazel