unix: patch packaging.tags in pip as well

Like setuptools, pip 20 also contains a copy of packaging.tags that
needs to be taught how to react when running from a statically linked
binary.

Closes #30.

cpython-unix/build-cpython.sh

@@ -197,6 +197,22 @@ diff --git a/src/pip/_internal/utils/glibc.py b/src/pip/_internal/utils/glibc.py
          gnu_get_libc_version = process_namespace.gnu_get_libc_version
      except AttributeError:
 
+diff --git a/src/pip/_vendor/packaging/tags.py b/src/pip/_vendor/packaging/tags.py
+index 60a69d8..08c0597 100644
+--- a/src/pip/_vendor/packaging/tags.py
++++ b/src/pip/_vendor/packaging/tags.py
+@@ -466,7 +466,10 @@ def _glibc_version_string_ctypes():
+     # which libc our process is actually using.
+     #
+     # Note: typeshed is wrong here so we are ignoring this line.
+-    process_namespace = ctypes.CDLL(None)  # type: ignore
++    try:
++        process_namespace = ctypes.CDLL(None)  # type: ignore
++    except OSError:
++        return None
+     try:
+         gnu_get_libc_version = process_namespace.gnu_get_libc_version
+     except AttributeError:
 EOF
 
 ${ROOT}/out/python/install/bin/python3 setup.py install