Add a script to build the android libraries

I'm not too fond of many of the hardcoded paths, but this is a good
first step. Once I get this working, I'll then improve it.

Author: vHanda

src/build-android.sh

@@ -0,0 +1,42 @@
+#!/bin/sh
+
+set -eux
+
+# Assumes Android Studio is installed on the standard path along with Android SDK/NDK
+export ANDROID_HOME=~/Library/Android/sdk/
+export ANDROID_NDK_HOME=~/Library/Android/sdk/ndk/$(ls $ANDROID_HOME/ndk | head -1)
+export JAVA_HOME=/Applications/Android\ Studio.app/Contents/jre/Contents/Home
+
+ROOTDIR=$(cd $(dirname $0); pwd -P)
+DISTDIR=$ROOTDIR/../android/
+TMPDIR=$ROOTDIR/tmp/android
+
+export PATH=$ANDROID_HOME/ndk/26.1.10909125/toolchains/llvm/prebuilt/darwin-x86_64/bin/:$ANDROID_HOME/platform-tools:$PATH
+
+rm -rf $DISTDIR/jniLibs $TMPDIR
+mkdir -p \
+    $DISTDIR \
+    $TMPDIR/armeabi-v7a \
+    $TMPDIR/arm64-v8a \
+    $TMPDIR/x86 \
+    $TMPDIR/x86_64
+
+ANDROID_SDK_VERSION=34
+CLANG_SUFFIX=-linux-android$ANDROID_SDK_VERSION-clang
+
+export GOOS=android
+export CGO_ENABLED=1
+
+GOARCH=arm CC=armv7a-linux-androideabi$ANDROID_SDK_VERSION-clang CXX=armv7a-linux-androideabi$ANDROID_SDK_VERSION-clang++ \
+    go build -v -x -buildmode=c-shared -trimpath -o=$TMPDIR/armeabi-v7a/go_git_dart.so
+GOARCH=arm64 CC=aarch64$CLANG_SUFFIX CXX=aarch64$CLANG_SUFFIX++ \
+    go build -v -x -buildmode=c-shared -trimpath -o=$TMPDIR/arm64-v8a/go_git_dart.so
+GOARCH=386 CC=i686$CLANG_SUFFIX CXX=i686$CLANG_SUFFIX++ \
+    go build -v -x -buildmode=c-shared -trimpath -o=$TMPDIR/x86/go_git_dart.so
+GOARCH=amd64 CC=x86_64$CLANG_SUFFIX CXX=x86_64$CLANG_SUFFIX++ \
+    go build -v -x -buildmode=c-shared -trimpath -o=$TMPDIR/x86_64/go_git_dart.so
+
+cp -rf $TMPDIR $DISTDIR/jniLibs
+find $DISTDIR -name "*.h" -exec rm {} \;
+rm -rf $DISTDIR/jniLibs/tmp
+