Bug 1825620 - pt5 - automatically create default config file if missing r=ng DONTBUILD

This is possible now that we default to storing the moz-libwebrtc
github repo in the STATE_DIR.

Depends on D175690

Differential Revision: https://phabricator.services.mozilla.com/D175691

dom/media/webrtc/third_party_build/use_config_env.sh

@@ -57,14 +57,8 @@ if [ "x$MOZ_CONFIG_PATH" = "x" ]; then
 fi
 
 if [ ! -f $MOZ_CONFIG_PATH ]; then
-  echo ""
-  echo "Missing $MOZ_CONFIG_PATH"
-  echo "Please copy $SCRIPT_DIR/example_config_env"
-  echo "and edit (at least) MOZ_LIBWEBRTC_SRC to match your environment."
-  echo ""
-  echo "cp $SCRIPT_DIR/example_config_env $MOZ_CONFIG_PATH"
-  echo ""
-  exit 1
+  echo "Creating default config file at $MOZ_CONFIG_PATH"
+  cp $SCRIPT_DIR/example_config_env $MOZ_CONFIG_PATH
 fi
 source $MOZ_CONFIG_PATH