Check if pip supports break systeem packages flag

This commit adds changes to be backwards compatible with older bullseye builders where pip does not yet support break system packages flag.

Makefile

@@ -5,14 +5,16 @@ PYTHON?=/usr/bin/python3
 COMMIT_HASH=$(shell git rev-parse --short HEAD)
 PACKAGES?=""
 REPO_CHANGED=$(shell if [ -d "./venv-$(COMMIT_HASH)" ]; then git status --porcelain | grep -c "scale_build/"; else echo "1"; fi)
+# Check if --break-system-packages flag is supported by pip
+BREAK_SYS_PKGS_FLAG=$(shell ${PYTHON} -m pip help install | grep -q -- '--break-system-packages' && echo "--break-system-packages" || echo "")
 
 .DEFAULT_GOAL := all
 
 check:
 ifneq ($(REPO_CHANGED),0)
 	@echo "Setting up new virtual environment"
 	@rm -rf venv-*
-	@${PYTHON} -m pip install --break-system-packages -U virtualenv >/dev/null || { echo "Failed to install/upgrade virtualenv package"; exit 1; }
+	@${PYTHON} -m pip install $(BREAK_SYS_PKGS_FLAG) -U virtualenv >/dev/null || { echo "Failed to install/upgrade virtualenv package"; exit 1; }
 	@${PYTHON} -m venv venv-${COMMIT_HASH} || { echo "Failed to create virutal environment"; exit 1; }
 	@{ . ./venv-${COMMIT_HASH}/bin/activate && \
 		python3 -m pip install -r requirements.txt >/dev/null 2>&1 && \