Added -ldflags=-s to the OSX cross-compile

There's a go 1.5 bug that requires this:
golang/go#11994

Author: Tudor Golubenco

docker/xgo-image/base/build.sh

@@ -103,7 +103,7 @@ CC=i686-w64-mingw32-gcc GOOS=windows GOARCH=386 CGO_ENABLED=1 go build $V -o $NA
 echo "Compiling for darwin/amd64..."
 CC=o64-clang HOST=x86_64-apple-darwin10 PREFIX=/usr/local $BUILD_DEPS /deps
 CC=o64-clang GOOS=darwin GOARCH=amd64 CGO_ENABLED=1 go get -d ./$PACK
-CC=o64-clang GOOS=darwin GOARCH=amd64 CGO_ENABLED=1 go build $V $R -o $NAME-darwin-amd64$R ./$PACK
+CC=o64-clang GOOS=darwin GOARCH=amd64 CGO_ENABLED=1 go build -ldflags=-s $V $R -o $NAME-darwin-amd64$R ./$PACK
 
 #echo "Compiling for darwin/386..."
 #CC=o32-clang HOST=i386-apple-darwin10 PREFIX=/usr/local $BUILD_DEPS /deps