Dockerfile: add support for USE_LOCAL (vlang#10953)

Dockerfile

@@ -3,11 +3,24 @@ FROM buildpack-deps:buster-curl
 
 LABEL maintainer="ANAGO Ronnel <anagoandy@gmail.com>"
 WORKDIR /opt/vlang
+
+ARG USE_LOCAL
+
 RUN apt-get update && \
     DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends gcc clang make git && \
     apt-get clean && rm -rf /var/cache/apt/archives/* && \
     rm -rf /var/lib/apt/lists/*
-COPY . .
+
+COPY . /vlang-local
+
+RUN if [ -z "${USE_LOCAL}" ] ; then \
+      git clone https://github.com/vlang/v/ /opt/vlang && \
+      rm -rf /vlang-local ; \
+    else \
+      mv /vlang-local/* . && \
+      rm -rf /vlang-local ; \
+    fi
+
 RUN make && \
     ln -s /opt/vlang/v /usr/local/bin/v