ci: build the in-tree SDCC and keep it between runs

The workflow and the Dockerfile install what building SDCC needs instead
of the distribution's sdcc, and the workflow caches toolchain/ keyed on
the contents of sdcc/.

.github/workflows/build.yml

@@ -29,7 +29,12 @@ jobs:
       - name: Install dependencies
         run: |
           apt update
-          apt install make gcc sdcc xxd python-is-python3 libjson-c-dev zlib1g-dev -y
+          apt install make gcc g++ bison flex libboost-dev patch bzip2 curl ca-certificates xxd python-is-python3 libjson-c-dev zlib1g-dev -y
+      - name: Cache the patched SDCC
+        uses: actions/cache@v4
+        with:
+          path: branch/toolchain
+          key: sdcc-${{ hashFiles('branch/sdcc/*') }}
       - name: Run the host-side unit tests
         run: cd branch && make -C test
       - name: Check that every machine definition can be compiled
@@ -41,7 +46,10 @@ jobs:
       - name: Make project with the health instrumentation
         run: cd branch && make clean && make CI=1 MACHINE="KP_9000_6XHML_X2" HEALTH=1
       - name: Make main
-        run: cd main && make CI=1 MACHINE="KP_9000_6XHML_X2" && cp output/KP_9000_6XHML_X2/rtlplayground.map /tmp/main.map
+        run: |
+          ln -s ../branch/toolchain main/toolchain
+          PATH="$(echo "$PWD"/branch/toolchain/sdcc-*/bin):$PATH"
+          cd main && make CI=1 MACHINE="KP_9000_6XHML_X2" && cp output/KP_9000_6XHML_X2/rtlplayground.map /tmp/main.map
       - name: Calculate bank growth
         run: |
           sed -rn 's/^([XCD]SEG|(BANK[0-9])).*=\s+([0-9]+)\. bytes.*$/MAIN_\1=\3/p' /tmp/main.map | sort -u >> "$GITHUB_ENV"