Make the distlib changes into a patch

tools/vendoring/patches/distlib.patch

@@ -0,0 +1,47 @@
+diff --git a/src/pip/_vendor/distlib/scripts.py b/src/pip/_vendor/distlib/scripts.py
+index cfa45d2af..e16292b83 100644
+--- a/src/pip/_vendor/distlib/scripts.py
++++ b/src/pip/_vendor/distlib/scripts.py
+@@ -49,6 +49,24 @@ if __name__ == '__main__':
+     sys.exit(%(func)s())
+ '''
+
++# Pre-fetch the contents of all executable wrapper stubs.
++# This is to address https://github.com/pypa/pip/issues/12666.
++# When updating pip, we rename the old pip in place before installing the
++# new version. If we try to fetch a wrapper *after* that rename, the finder
++# machinery will be confused as the package is no longer available at the
++# location where it was imported from. So we load everything into memory in
++# advance.
++
++# Issue 31: don't hardcode an absolute package name, but
++# determine it relative to the current package
++distlib_package = __name__.rsplit('.', 1)[0]
++
++WRAPPERS = {
++    r.name: r.bytes
++    for r in finder(distlib_package).iterator("")
++    if r.name.endswith(".exe")
++}
++
+
+ def enquote_executable(executable):
+     if ' ' in executable:
+@@ -409,15 +427,11 @@ class ScriptMaker(object):
+                 bits = '32'
+             platform_suffix = '-arm' if get_platform() == 'win-arm64' else ''
+             name = '%s%s%s.exe' % (kind, bits, platform_suffix)
+-            # Issue 31: don't hardcode an absolute package name, but
+-            # determine it relative to the current package
+-            distlib_package = __name__.rsplit('.', 1)[0]
+-            resource = finder(distlib_package).find(name)
+-            if not resource:
++            if name not in WRAPPERS:
+                 msg = ('Unable to find resource %s in package %s' %
+                        (name, distlib_package))
+                 raise ValueError(msg)
+-            return resource.bytes
++            return WRAPPERS[name]
+
+     # Public API follows
+