Enable -dead_strip by default for opt builds

This change makes `-dead_strip` always be enabled for `opt` builds,
regardless of `--objc_enable_binary_stripping`. This should be the right
default for everyone, if not we can look at adding a way to disable it.

This also allows passing `--features=dead_strip` to enable `-dead_strip`
in other configurations, which previously wasn't supported if you
weren't using `opt`.

crosstool/cc_toolchain_config.bzl

@@ -979,6 +979,11 @@ def _impl(ctx):
                     ),
                 ],
             ),
+            flag_set(
+                actions = _DYNAMIC_LINK_ACTIONS,
+                flag_groups = [flag_group(flags = ["-dead_strip"])],
+                with_features = [with_feature_set(features = ["opt"])],
+            ),
         ],
     )
 
@@ -1990,14 +1995,9 @@ def _impl(ctx):
         flag_sets = [
             flag_set(
                 actions = _DYNAMIC_LINK_ACTIONS,
-                flag_groups = [
-                    flag_group(
-                        flags = ["-dead_strip"],
-                    ),
-                ],
+                flag_groups = [flag_group(flags = ["-dead_strip"])],
             ),
         ],
-        requires = [feature_set(features = ["opt"])],
     )
 
     oso_prefix_feature = feature(

test/linking_tests.bzl

@@ -7,6 +7,21 @@ load(
 
 default_test = make_action_command_line_test_rule()
 
+opt_test = make_action_command_line_test_rule(
+    config_settings = {
+        "//command_line_option:compilation_mode": "opt",
+    },
+)
+
+dead_strip_requested_test = make_action_command_line_test_rule(
+    config_settings = {
+        "//command_line_option:compilation_mode": "fastbuild",
+        "//command_line_option:features": [
+            "dead_strip",
+        ],
+    },
+)
+
 disable_objc_test = make_action_command_line_test_rule(
     config_settings = {
         "//command_line_option:features": [
@@ -26,6 +41,39 @@ def linking_test_suite(name):
             "2",
             "-ObjC",
         ],
+        not_expected_argv = [
+            "-dead_strip",
+        ],
+        mnemonic = "ObjcLink",
+        target_under_test = "//test/test_data:apple_binary",
+    )
+
+    opt_test(
+        name = "{}_opt_link_test".format(name),
+        tags = [name],
+        expected_argv = [
+            "-Xlinker",
+            "-objc_abi_version",
+            "-Xlinker",
+            "2",
+            "-ObjC",
+            "-dead_strip",
+        ],
+        mnemonic = "ObjcLink",
+        target_under_test = "//test/test_data:apple_binary",
+    )
+
+    dead_strip_requested_test(
+        name = "{}_dead_strip_requested_test".format(name),
+        tags = [name],
+        expected_argv = [
+            "-Xlinker",
+            "-objc_abi_version",
+            "-Xlinker",
+            "2",
+            "-ObjC",
+            "-dead_strip",
+        ],
         mnemonic = "ObjcLink",
         target_under_test = "//test/test_data:apple_binary",
     )