Make doctests only compatible with x86_64

For some reason doctests only work on x86_64. Added a TODO
to investigate further.

Change-Id: I38cfb30e8832d6cfd5f9e67385d9c4cbe950a5f6
Signed-off-by: James Kuszmaul <james.kuszmaul@bluerivertech.com>
diff --git a/tools/rust/defs.bzl b/tools/rust/defs.bzl
index 06f1ad1..0093184 100644
--- a/tools/rust/defs.bzl
+++ b/tools/rust/defs.bzl
@@ -8,12 +8,13 @@
     _rust_test = "rust_test",
 )
 
-def rust_doc_test(target_compatible_with = ["//tools/platforms/rust:has_support"], tags = [], **kwargs):
+def rust_doc_test(tags = [], **kwargs):
     # TODO(james): Attempting to execute this remotely results
     # in complaints about overly large files.
     _rust_doc_test(
         tags = tags + ["no-remote-exec"],
-        target_compatible_with = target_compatible_with,
+        # TODO(adam.snaider): Investigate why doctests only work on x86_64.
+        target_compatible_with = ["@platforms//cpu:x86_64"],
         **kwargs
     )