Add script to build Google.Protobuf.Tools for csharp.

csharp/build_tools.sh

+#!/bin/bash
+
+if [ $# -ne 1 ]; then
+  cat <<EOF
+Usage: $0 <VERSION_NUMBER>
+
+Example:
+  $ $0 3.0.0
+
+This script will download pre-built protoc binaries from maven repository and
+create the Google.Protobuf.Tools package. Well-known type .proto files will also
+be included.
+EOF
+  exit 1
+fi
+
+VERSION_NUMBER=$1
+# <directory name> <binary file name> pairs.
+declare -a FILE_NAMES=(          \
+  windows_x86 windows-x86_32.exe \
+  windows_x64 windows-x86_64.exe \
+  macosx_x86  osx-x86_32.exe     \
+  macosx_x64  osx-x86_64.exe     \
+  linux_x86   linux-x86_32.exe   \
+  linux_x64   linux-x86_64.exe   \
+)
+
+set -e
+
+mkdir -p protoc
+# Create a zip file for each binary.
+for((i=0;i<${#FILE_NAMES[@]};i+=2));do
+  DIR_NAME=${FILE_NAMES[$i]}
+  mkdir -p protoc/$DIR_NAME
+
+  if [ ${DIR_NAME:0:3} = "win" ]; then
+    TARGET_BINARY="protoc.exe"
+  else
+    TARGET_BINARY="protoc"
+  fi
+
+  BINARY_NAME=${FILE_NAMES[$(($i+1))]}
+  BINARY_URL=http://repo1.maven.org/maven2/com/google/protobuf/protoc/${VERSION_NUMBER}/protoc-${VERSION_NUMBER}-${BINARY_NAME}
+
+  if ! wget ${BINARY_URL} -O protoc/$DIR_NAME/$TARGET_BINARY &> /dev/null; then
+    echo "[ERROR] Failed to download ${BINARY_URL}" >&2
+    echo "[ERROR] Skipped $protoc-${VERSION_NAME}-${DIR_NAME}" >&2
+    continue
+  fi
+done
+
+nuget pack Google.Protobuf.Tools.nuspec