Dockerfile: reduce size of resulting image

This reduces the size of the Docker image from 13GB to 1.71GB, and
should therefore make CI of the drivers package much faster. It should
hopefully also avoid the out-of-space problem we currently have when
building the smoke tests for the drivers repo.

 This size reduction is done by using multistage builds and only copying
 the necessary files in the final stage.

Dockerfile

@@ -20,26 +20,24 @@ FROM tinygo-llvm AS tinygo-llvm-build
 RUN cd /tinygo/ && \
     make llvm-build
 
-# tinygo-compiler stage builds the compiler itself
-FROM tinygo-llvm-build AS tinygo-compiler
+# tinygo-compiler-build stage builds the compiler itself
+FROM tinygo-llvm-build AS tinygo-compiler-build
 
 COPY . /tinygo
 
-# update submodules
+# build the compiler and tools
 RUN cd /tinygo/ && \
-    rm -rf ./lib/*/ && \
-    git submodule sync && \
-    git submodule update --init --recursive --force
-
-RUN cd /tinygo/ && \
-    make
+    git submodule update --init --recursive && \
+    make gen-device -j4 && \
+    make build/release
 
-# tinygo-tools stage installs the needed dependencies to compile TinyGo programs for all platforms.
-FROM tinygo-compiler AS tinygo-tools
+# tinygo-compiler copies the compiler build over to a base Go container (without
+# all the build tools etc).
+FROM golang:1.21 AS tinygo-compiler
 
-RUN cd /tinygo/ && \
-    make wasi-libc binaryen && \
-    make gen-device -j4 && \
-    cp build/* $GOPATH/bin/
+# Copy tinygo build.
+COPY --from=tinygo-compiler-build /tinygo/build/release/tinygo /tinygo
 
+# Configure the container.
+ENV PATH="${PATH}:/tinygo/bin"
 CMD ["tinygo"]