Disable XNNPACK workspace sharing by default (#6199)

Summary:
Pull Request resolved: #6199

Disable workspace sharing by default. There is currently a crash that occurs when workspace sharing is enabled when freeing the delegate. This change will increase ET memory usage, but needs to be done until we address the root cause. After we are confident that it is fixed, we will revert this change.

Reviewed By: kirklandsign

Differential Revision: D64352037

fbshipit-source-id: 7fcebcea01d9b41d7fb4b884c37902f8617a31f9

Author: GregoryComer

backends/xnnpack/targets.bzl

@@ -6,7 +6,7 @@ def _get_preprocessor_flags():
     Disable if someone explictly specified a config option,
     else Enable otherwise
     """
-    if native.read_config("executorch", "xnnpack_workspace_sharing", "1") == "0":
+    if native.read_config("executorch", "xnnpack_workspace_sharing", "0") == "0":
         return []
 
     # Enable if not disabled through config