ci: Update workflows/scripts for deploying collab to use clang (#51224)

Release Notes:

- N/A

Dockerfile-collab

@@ -14,8 +14,12 @@ ARG GITHUB_SHA
 ENV GITHUB_SHA=$GITHUB_SHA
 
 # Also add `cmake`, since we need it to build `wasmtime`.
+# clang is needed because `webrtc-sys` uses Clang-specific compiler flags.
 RUN apt-get update; \
-    apt-get install -y --no-install-recommends cmake
+    apt-get install -y --no-install-recommends cmake clang
+
+ENV CC=clang
+ENV CXX=clang++
 
 RUN --mount=type=cache,target=./script/node_modules \
     --mount=type=cache,target=/usr/local/cargo/registry \