Add target_compatible_with parameter to proto_toolchain in Bazel rules (#22429)

In some cases, few targets can require different proto_toolchains.

In my case, my project defines different toolchains and each of them can define its own Protobuf compiler from its SDK, independent of the others. Restricting it with exec_compatible_with is not an option, since each target is built on the same x86_64 system.

I patched this Bazel file in my build system and thus was able to define the Protobuf compiler independently for each target.

Closes #22429

COPYBARA_INTEGRATE_REVIEW=#22429 from jagub2:proto_toolchain_target_compatibility 6539aad
PiperOrigin-RevId: 785828194

Author: jagub2

bazel/toolchains/proto_toolchain.bzl

@@ -13,7 +13,7 @@ The macro additionally creates toolchain target when toolchain_type is given.
 load("//bazel/private:proto_toolchain_rule.bzl", _proto_toolchain_rule = "proto_toolchain")
 load("//bazel/private:toolchain_helpers.bzl", "toolchains")
 
-def proto_toolchain(*, name, proto_compiler, exec_compatible_with = []):
+def proto_toolchain(*, name, proto_compiler, exec_compatible_with = [], target_compatible_with = []):
     """Creates a proto_toolchain and toolchain target for proto_library.
 
     Toolchain target is suffixed with "_toolchain".
@@ -22,13 +22,14 @@ def proto_toolchain(*, name, proto_compiler, exec_compatible_with = []):
       name: name of the toolchain
       proto_compiler: (Label) of either proto compiler sources or prebuild binaries
       exec_compatible_with: ([constraints]) List of constraints the prebuild binary is compatible with.
+      target_compatible_with: ([constraints]) List of constraints the target it is compatible with.
     """
     _proto_toolchain_rule(name = name, proto_compiler = proto_compiler)
 
     native.toolchain(
         name = name + "_toolchain",
         toolchain_type = toolchains.PROTO_TOOLCHAIN,
         exec_compatible_with = exec_compatible_with,
-        target_compatible_with = [],
+        target_compatible_with = target_compatible_with,
         toolchain = name,
     )