build/release: create new release package for reproducible builds

In this commit, we create a new `build/release` package which houses the
build instructions and scripts that we need to do deterministic builds
across Windows, Linux, and MacOS.

With this new system, it's now possible for all `lnd` developers, as
well as users to verify the posted build binaries. This wasn't possible
in prior release as only in Go 1.13 did deterministic builds becomes
easier/possible. See the new `README.md` for further details.

build/release/README.md

@@ -0,0 +1,34 @@
+# lnd's Reproducible Build System
+
+This package contains the buidl script that the `lnd` project uses in order to
+build binaries for each new release. As of Go 1.13, with some new build flags,
+binaries are now reproducible, allowing developers to build the binary on
+distinct machines, and end up with a byte-for-byte identical binary.  However,
+this wasn't _fully_ solved in Go 1.13, as the build system still includes the
+directory the binary is built into the binary itself. As a result, our scripts
+utilize a work around needed until Go 1.13.2.  
+
+## Building a New Release
+
+### MacOS/Linux/Windows (WSL)
+
+No prior set up is needed on Linux or MacOS is required in order to build the
+release binaries.  However, on Windows, the only way to build the binaries atm
+is using the Windows Subsystem Linux. One can build the release binaries from
+one's `lnd` directory, no matter where it's located.  One can download `lnd` to
+
+```
+git clone https://github.com/lightningnetwork/lnd.git
+```
+
+Afterwards, the release manager/verifier simply needs to run:
+`./build/release/release.sh <TAG>` (from the top-level `lnd` directory) , where
+`<TAG>` is the name of the next release/tag.
+
+## Verifying a Release
+
+With Go 1.13, it's now possible for third parties to verify a release binary.
+Before this release, one had to trust that release manager to build the proper
+binary. With this new system, third parties can now _independently_ run the
+release process, and verify that all the hashes in the final `manifest.txt`
+match up.

build/release/release.sh

@@ -0,0 +1,78 @@
+#!/bin/bash
+
+# Simple bash script to build basic lnd tools for all the platforms
+# we support with the golang cross-compiler.
+#
+# Copyright (c) 2016 Company 0, LLC.
+# Use of this source code is governed by the ISC
+# license.
+
+set -e
+
+# If no tag specified, use date + version otherwise use tag.
+if [[ $1x = x ]]; then
+    DATE=`date +%Y%m%d`
+    VERSION="01"
+    TAG=$DATE-$VERSION
+else
+    TAG=$1
+fi
+
+go mod vendor
+tar -cvzf vendor.tar.gz vendor
+
+PACKAGE=lnd
+MAINDIR=$PACKAGE-$TAG
+mkdir -p $MAINDIR
+
+cp vendor.tar.gz $MAINDIR/
+rm vendor.tar.gz
+rm -r vendor
+
+PACKAGESRC="$MAINDIR/$PACKAGE-source-$TAG.tar"
+git archive -o $PACKAGESRC HEAD
+gzip -f $PACKAGESRC > "$PACKAGESRC.gz"
+
+cd $MAINDIR
+
+# If LNDBUILDSYS is set the default list is ignored. Useful to release
+# for a subset of systems/architectures.
+SYS=${LNDBUILDSYS:-"windows-386 windows-amd64 openbsd-386 openbsd-amd64 linux-386 linux-amd64 linux-armv6 linux-armv7 linux-arm64 darwin-386 darwin-amd64 dragonfly-amd64 freebsd-386 freebsd-amd64 freebsd-arm netbsd-386 netbsd-amd64 linux-mips64 linux-mips64le linux-ppc64"}
+
+# Use the first element of $GOPATH in the case where GOPATH is a list
+# (something that is totally allowed).
+PKG="github.com/lightningnetwork/lnd"
+COMMIT=$(git describe --abbrev=40 --dirty)
+COMMITFLAGS="-X $PKG/build.Commit=$COMMIT"
+
+for i in $SYS; do
+    OS=$(echo $i | cut -f1 -d-)
+    ARCH=$(echo $i | cut -f2 -d-)
+    ARM=
+
+    if [[ $ARCH = "armv6" ]]; then
+      ARCH=arm
+      ARM=6
+    elif [[ $ARCH = "armv7" ]]; then
+      ARCH=arm
+      ARM=7
+    fi
+
+    mkdir $PACKAGE-$i-$TAG
+    cd $PACKAGE-$i-$TAG
+
+    echo "Building:" $OS $ARCH $ARM
+    env CGO_ENABLED=0 GOOS=$OS GOARCH=$ARCH GOARM=$ARM go build -v -trimpath -ldflags="-s -w -buildid= $COMMITFLAGS" -tags="autopilotrpc signrpc walletrpc chainrpc invoicesrpc routerrpc watchtowerrpc" github.com/lightningnetwork/lnd/cmd/lnd
+    env CGO_ENABLED=0 GOOS=$OS GOARCH=$ARCH GOARM=$ARM go build -v -trimpath -ldflags="-s -w -buildid= $COMMITFLAGS" -tags="autopilotrpc invoicesrpc walletrpc routerrpc watchtowerrpc" github.com/lightningnetwork/lnd/cmd/lncli
+    cd ..
+
+    if [[ $OS = "windows" ]]; then
+	zip -r $PACKAGE-$i-$TAG.zip $PACKAGE-$i-$TAG
+    else
+	tar -cvzf $PACKAGE-$i-$TAG.tar.gz $PACKAGE-$i-$TAG
+    fi
+
+    rm -r $PACKAGE-$i-$TAG
+done
+
+shasum -a 256 * > manifest-$TAG.txt