Get update-dependenices working again

- Fix build issues due to .props file not existing on a clean
  enlistment
- Fix path separator issues on *NIX
- Add update-dependencies.sh
- Support -Update in update-dependencies.ps1

build_projects/update-dependencies/update-dependencies.sh

@@ -0,0 +1,63 @@
+#!/usr/bin/env bash
+#
+# Copyright (c) .NET Foundation and contributors. All rights reserved.
+# Licensed under the MIT license. See LICENSE file in the project root for full license information.
+#
+
+set -e
+
+SOURCE="${BASH_SOURCE[0]}"
+while [ -h "$SOURCE" ]; do # resolve $SOURCE until the file is no longer a symlink
+  DIR="$( cd -P "$( dirname "$SOURCE" )" && pwd )"
+  SOURCE="$(readlink "$SOURCE")"
+  [[ "$SOURCE" != /* ]] && SOURCE="$DIR/$SOURCE" # if $SOURCE was a relative symlink, we need to resolve it relative to the path where the symlink file was located
+done
+DIR="$( cd -P "$( dirname "$SOURCE" )" && pwd )"
+
+REPO_ROOT="$DIR/../.."
+PROJECT_PATH="$DIR/update-dependencies.csproj"
+
+# Some things depend on HOME and it may not be set. We should fix those things, but until then, we just patch a value in
+if [ -z "${HOME:-}" ]; then
+    export HOME=$REPO_ROOT/artifacts/home
+
+    [ ! -d "$HOME" ] || rm -Rf "$HOME"
+    mkdir -p "$HOME"
+fi
+
+# Use a repo-local install directory (but not the artifacts directory because that gets cleaned a lot)
+if [ -z "${DOTNET_INSTALL_DIR:-}" ]; then
+   export DOTNET_INSTALL_DIR=$REPO_ROOT/.dotnet_stage0/x64
+fi
+
+# Install a stage 0
+echo "Installing .NET Core CLI Stage 0"
+$REPO_ROOT/scripts/obtain/dotnet-install.sh -Channel master -Architecture x64
+
+if [ $? -ne 0 ]; then
+    echo "Failed to install stage 0"
+    exit 1
+fi
+
+# Put the stage 0 on the path
+export PATH=$DOTNET_INSTALL_DIR:$PATH
+
+# Generate some props files that are imported by update-dependencies
+echo "Generating property files..."
+dotnet msbuild "$REPO_ROOT/build.proj" /p:Architecture=x64 /p:GeneratingPropsFile=true /t:WriteDynamicPropsToStaticPropsFiles
+
+echo "Resotring $PROJECT_PATH..."
+dotnet restore "$PROJECT_PATH"
+
+if [ $? -ne 0 ]; then
+    echo "Failed to restore"
+    exit 1
+fi
+
+echo "Invoking App $PROJECT_PATH..."
+dotnet run -p "$PROJECT_PATH" $@
+
+if [ $? -ne 0 ]; then
+    echo "Build failed"
+    exit 1
+fi