Added RISC-V continuous integration script (#327)

* Fixes for RISCV build

* Consolidate compiler flags

* Added RISC-V continuous integration script
Co-authored-by: NAdvait Jain <advaitjain@users.noreply.github.com>

tensorflow/lite/micro/tools/ci_build/test_riscv.sh

+#!/usr/bin/env bash
+# Copyright 2021 The TensorFlow Authors. 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.
+# ==============================================================================
+#
+# Tests the RISC-V MCU platform for the SiFive FE310.
+
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+ROOT_DIR=${SCRIPT_DIR}/../../../../..
+cd "${ROOT_DIR}"
+pwd
+
+source tensorflow/lite/micro/tools/ci_build/helper_functions.sh
+
+TARGET=mcu_riscv
+
+readable_run make -f tensorflow/lite/micro/tools/make/Makefile TARGET=${TARGET} third_party_downloads
+
+readable_run make -f tensorflow/lite/micro/tools/make/Makefile clean
+
+# Validate build for libtensorflow-microlite.a
+readable_run make -j8 -f tensorflow/lite/micro/tools/make/Makefile TARGET=${TARGET}
+
+# Make sure an example will build.
+readable_run make -j8 -f tensorflow/lite/micro/tools/make/Makefile TARGET=${TARGET} hello_world
+
+# There are currently no runtime tests, we only check that compilation is working.