[bazel] Enable dead code stripping on macOS

src/workerd/server/BUILD.bazel

@@ -10,6 +10,18 @@ config_setting(
     constraint_values = ["@platforms//os:linux"],
 )
 
+config_setting(
+    name = "is_opt",
+    values = {"compilation_mode": "opt"},
+)
+
+# bazel enables the --ffunction-sections, --gc-sections flags used to remove dead code by default
+# on Linux opt builds. Define the equivalent macOS flag -Wl,-dead_strip if optimization is enabled.
+selects.config_setting_group(
+    name = "use_dead_strip",
+    match_all = ["@platforms//os:macos", "is_opt"],
+)
+
 # Flag that can be used to force-disable tcmalloc. Mainly used for ASAN builds.
 # TODO(cleanup): This feels ugly but I've exceeded my timebox for fighting Bazel for now.
 bool_flag(
@@ -39,6 +51,10 @@ wd_cc_binary(
         ":really_use_tcmalloc": "@com_google_tcmalloc//tcmalloc",
         "//conditions:default": "@bazel_tools//tools/cpp:malloc",
     }),
+    linkopts = select({
+        ":use_dead_strip": ["-Wl,-dead_strip"],
+        "//conditions:default": [""],
+    }),
 )
 
 wd_cc_library(