Tools in local-only genrule are not built with the correct local exec platform

### Description of the bug:

Internally we have a macro with a genrule like this

```python
def some_macro(name, ...):
...
native.genrule(
name = name,
...
cmd = "$(location //tools/my_tool) ...",
local = True,
tags = ["manual"],
tools = [
"//tools/my_tool",
],
)
```

this runs fine on a local-exec build. However, using a remote exec where host=MacOS/arm64 and exec+target=linux/amd64 would cause this genrule to use a linux/amd64 version of `//tools/my_tool`.

We fixed this by adding

```diff
@@ -1,3 +1,5 @@
+load("@local_config_platform//:constraints.bzl", "HOST_CONSTRAINTS")
+
...
+ exec_compatible_with = HOST_CONSTRAINTS,
```

to the genrule to force it to use a MacOS/arm64 version of `//tools/my_tool`.

I think it would make sense for this exec_compatible_with to be applied automatically when `local = True` is set.

### Which category does this issue belong to?

Configurability

### What's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

_No response_

### Which operating system are you running Bazel on?

7.4.1

### What is the output of `bazel info release`?

_No response_

### If `bazel info release` returns `development version` or `(@non-git)`, tell us how you built Bazel.

_No response_

### What's the output of `git remote get-url origin; git rev-parse HEAD` ?

```text

```

### If this is a regression, please try to identify the Bazel commit where the bug was introduced with bazelisk --bisect.

_No response_

### Have you found anything relevant by searching the web?

_No response_

### Any other information, logs, or outputs that you want to share?

_No response_

Start at Bazel's genrule implementation and the platform-selection path used when local=True; compare it with the explicit exec_compatible_with=HOST_CONSTRAINTS workaround in the issue. Done means a local-only genrule selects the host-compatible tool under the described MacOS/arm64 and Linux/amd64 configuration, with coverage for the cross-platform case.

Written by the indexing model from the issue text.