Update apple_support to 1.20.0

[mattrobmattrob]

ERROR: /Users/administrator/buildbuddy.noindex/remote_build/8fab8d97-3f6f-4e43-92c2-a2c82b58bcae/repo-root/tools/swiftc_stub/BUILD:19:31: in macos_command_line_application rule //tools/swiftc_stub:swiftc:
Traceback (most recent call last):
        File "/Users/administrator/buildbuddy.noindex/remote_build/8fab8d97-3f6f-4e43-92c2-a2c82b58bcae/repo-root/bazel-output-base/external/rules_apple+/apple/internal/macos_rules.bzl", line 2002, column 65, in _macos_command_line_application_impl
                link_result = linking_support.register_binary_linking_action(
        File "/Users/administrator/buildbuddy.noindex/remote_build/8fab8d97-3f6f-4e43-92c2-a2c82b58bcae/repo-root/bazel-output-base/external/rules_apple+/apple/internal/linking_support.bzl", line 525, column 46, in _register_binary_linking_action
                linking_outputs = _link_multi_arch_binary(
        File "/Users/administrator/buildbuddy.noindex/remote_build/8fab8d97-3f6f-4e43-92c2-a2c82b58bcae/repo-root/bazel-output-base/external/rules_apple+/apple/internal/linking_support.bzl", line 197, column 53, in _link_multi_arch_binary
                split_target_triplets = get_split_target_triplet(ctx)
        File "/Users/administrator/buildbuddy.noindex/remote_build/8fab8d97-3f6f-4e43-92c2-a2c82b58bcae/repo-root/bazel-output-base/external/rules_apple+/apple/internal/multi_arch_binary_support.bzl", line 103, column 59, in get_split_target_triplet
                result[split_transition_key] = _get_target_triplet(config)
        File "/Users/administrator/buildbuddy.noindex/remote_build/8fab8d97-3f6f-4e43-92c2-a2c82b58bcae/repo-root/bazel-output-base/external/rules_apple+/apple/internal/multi_arch_binary_support.bzl", line 79, column 75, in _get_target_triplet
                cpu_platform = apple_common.apple_platform.for_target_cpu(apple_common.get_cpu(config))
Error: 'struct' value has no field or method 'get_cpu'
Available attributes: Objc, XcodeProperties, XcodeVersionConfig, apple_host_system_env, apple_platform, apple_toolchain, compilation_support, dotted_version, get_apple_config, get_split_build_configs, get_split_prerequisites, new_objc_provider, platform, platform_type, target_apple_env

[mattrobmattrob]

Needs bazelbuild/rules_apple#2670 instead.

[luispadron]

Doing this over in #3163