add android build target

Makefile

@@ -5,6 +5,9 @@ BUILDOPTS = -a -tags netgo
 LDFLAGS = -ldflags '-s -w -extldflags "-static" -X main.version=$(VERSION)'
 LDFLAGS_NATIVE = -ldflags '-s -w -X main.version=$(VERSION)'
 
+NDK_CC_ARM = $(abspath ../../ndk-toolchain-arm/bin/arm-linux-androideabi-gcc)
+NDK_CC_ARM64 = $(abspath ../../ndk-toolchain-arm64/bin/aarch64-linux-android21-clang)
+
 GO := go
 
 src = $(wildcard *.go)
@@ -17,6 +20,9 @@ all: bin-linux-amd64 bin-linux-386 bin-linux-arm \
 	bin-darwin-amd64 bin-darwin-arm64 \
 	bin-windows-amd64 bin-windows-386 bin-windows-arm
 
+allplus: all \
+	bin-android-arm bin-android-arm64
+
 bin-native: $(OUTSUFFIX)
 bin-linux-amd64: $(OUTSUFFIX).linux-amd64
 bin-linux-386: $(OUTSUFFIX).linux-386
@@ -33,6 +39,8 @@ bin-darwin-arm64: $(OUTSUFFIX).darwin-arm64
 bin-windows-amd64: $(OUTSUFFIX).windows-amd64.exe
 bin-windows-386: $(OUTSUFFIX).windows-386.exe
 bin-windows-arm: $(OUTSUFFIX).windows-arm.exe
+bin-android-arm: $(OUTSUFFIX).android-arm
+bin-android-arm64: $(OUTSUFFIX).android-arm64
 
 $(OUTSUFFIX): $(src)
 	$(GO) build $(LDFLAGS_NATIVE) -o $@
@@ -82,6 +90,12 @@ $(OUTSUFFIX).windows-386.exe: $(src)
 $(OUTSUFFIX).windows-arm.exe: $(src)
 	CGO_ENABLED=0 GOOS=windows GOARCH=arm GOARM=7 $(GO) build $(BUILDOPTS) $(LDFLAGS) -o $@
 
+$(OUTSUFFIX).android-arm: $(src)
+	CC=$(NDK_CC_ARM) CGO_ENABLED=1 GOOS=android GOARCH=arm GOARM=7 $(GO) build $(LDFLAGS_NATIVE) -o $@
+
+$(OUTSUFFIX).android-arm64: $(src)
+	CC=$(NDK_CC_ARM64) CGO_ENABLED=1 GOOS=android GOARCH=arm64 $(GO) build $(LDFLAGS_NATIVE) -o $@
+
 clean:
 	rm -f bin/*
 
@@ -102,6 +116,13 @@ install:
 	bin-freebsd-amd64 \
 	bin-freebsd-386 \
 	bin-freebsd-arm \
+	bin-netbsd-amd64 \
+	bin-netbsd-386 \
+	bin-openbsd-amd64 \
+	bin-openbsd-386 \
 	bin-darwin-amd64 \
 	bin-windows-amd64 \
-	bin-windows-386
+	bin-windows-386 \
+	bin-windows-arm \
+	bin-android-arm \
+	bin-android-arm64