fix codeql complaining about missing cython

backports commits 6cbb7d6, 142bb0e, 4df8255, and 30c145e

.github/workflows/codeql-analysis.yml

@@ -33,7 +33,10 @@ jobs:
       with:
         # just fetching 1 commit is not enough for setuptools-scm, so we fetch all
         fetch-depth: 0
-
+    - name: Set up Python
+      uses: actions/setup-python@v2
+      with:
+        python-version: 3.8
     # Initializes the CodeQL tools for scanning.
     - name: Initialize CodeQL
       uses: github/codeql-action/init@v1
@@ -59,7 +62,7 @@ jobs:
     - name: Install requirements, build and install Borg
       run: |
        sudo apt-get update
-       sudo apt-get install libacl1-dev
+       sudo apt-get install -y libacl1-dev
        pip3 install -r requirements.d/development.txt
        pip3 install -e .
 

pyproject.toml

@@ -0,0 +1,3 @@
+[build-system]
+requires = ["setuptools", "pkgconfig", "Cython!=0.27"]
+build-backend = "setuptools.build_meta"

setup.py

@@ -19,6 +19,7 @@ try:
 except ImportError:
     cythonize = None
 
+sys.path += [os.path.dirname(__file__)]
 import setup_checksums
 import setup_compress
 import setup_crypto