ci: build elc from dist/platform/elc.c with system curl/ssl headers

elc-bootstrap.c isn't committed to engram-lang; the actual C source
is dist/platform/elc.c. Add libcurl4-openssl-dev/libssl-dev install
step so cc has the right headers.

.gitea/workflows/deploy.yaml

@@ -74,16 +74,20 @@ jobs:
       - name: Configure docker auth for Artifact Registry
         run: gcloud auth configure-docker us-central1-docker.pkg.dev --quiet
 
+      - name: Install C build deps for elc
+        run: |
+          sudo apt-get update -qq
+          sudo apt-get install -y --no-install-recommends build-essential libcurl4-openssl-dev libssl-dev
+
       - name: Build elc fresh on the runner
         run: |
           set -euo pipefail
-          # The committed dist/platform/elc may be from a different architecture
-          # (e.g. Will's macOS arm64 dev box). Compile from elc-bootstrap.c on
-          # the runner so the binary matches linux/amd64.
+          # The committed dist/platform/elc is arm64 from Will's mac. We
+          # rebuild from dist/platform/elc.c (the canonical C source) so
+          # the binary matches the runner's linux/amd64.
           cd "$EL_HOME"
-          mkdir -p dist/platform
           cc -O2 -o dist/platform/elc \
-            dist/elc-bootstrap.c \
+            dist/platform/elc.c \
             el-compiler/runtime/el_runtime.c \
             -I el-compiler/runtime \
             -lcurl -lpthread -ldl -lm -lssl -lcrypto