Hide fb-isms from OSS buck2 graph (#2192)

Summary: Pull Request resolved: facebook/folly#2192

Test Plan: This, combined with several other changes, will eventually make folly build using buck2 in OSS

Reviewed By: Gownta

Differential Revision: D57165718

Pulled By: bigfootjon

fbshipit-source-id: 66f62d04d8f68808e4b37fadef68f0f220e23ea7

third-party/folly/src/.buckconfig

@@ -8,10 +8,11 @@ none = none
 [cell_aliases]
 config = prelude
 ovr_config = prelude
-fbcode = none
-fbsource = none
+fbcode = shim
+fbsource = shim
 fbcode_macros = shim
 buck = none
+bazel_skylib = shim
 
 [parser]
 target_platform_detector_spec = target:root//...->prelude//platforms:default