Make hermetic interpreters compatible to disallow_empty_glob (#761)

A single filegroup is used to aggregate the interpreter files.
Its platform specific regex patterns are not compatible to the flag
`--incompatible_disallow_empty_glob` which forbids any pattern to return
an empty list. For example, on a Linux host the `"*.exe",` will be empty.

python/repositories.bzl

diff --git a/python/repositories.bzl b/python/repositories.bzl
index 1441432..5061078 100644
--- a/python/repositories.bzl
+++ b/python/repositories.bzl
@@ -140,6 +140,8 @@
             "Scripts/**",
             "share/**",
         ],
+        # Platform-agnostic filegroup can't match on all patterns.
+        allow_empty = True,
         exclude = [
             "**/* *", # Bazel does not support spaces in file names.
         ],