alpine: add `bash` to Dockerfile.alpine; also set VFLAGS="-cc gcc" in that environment

Dockerfile.alpine

@@ -6,11 +6,12 @@ WORKDIR /opt/vlang
 
 ENV VVV  /opt/vlang
 ENV PATH /opt/vlang:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+ENV VFLAGS -cc gcc
 
 RUN mkdir -p /opt/vlang && ln -s /opt/vlang/v /usr/bin/v
 
 RUN apk --no-cache add \
-  git make upx gcc \
+  git make upx gcc bash \
   musl-dev \
   openssl-dev sqlite-dev \
   libx11-dev glfw-dev freetype-dev