systemlibs: unbundle typing_extensions

Signed-off-by: Jason Zaman <jason@perfinion.com>

third_party/systemlibs/syslibs_configure.bzl

@@ -44,6 +44,7 @@ VALID_LIBS = [
     "snappy",
     "tblib_archive",
     "termcolor_archive",
+    "typing_extensions_archive",
     "wrapt",
     "zlib",
 ]

third_party/systemlibs/typing_extensions.BUILD

@@ -0,0 +1,16 @@
+# Description:
+#   Backports for the typing module to older Python versions. See
+#   https://github.com/python/typing/blob/master/typing_extensions/README.rst
+
+licenses(["notice"])  # PSF
+
+py_library(
+    name = "typing_extensions",
+    srcs_version = "PY2AND3",
+    visibility = ["//visibility:public"],
+)
+
+filegroup(
+    name = "LICENSE",
+    visibility = ["//visibility:public"],
+)