Allow unused parameters in the stdlib build

Previously, the stdlib would fail to build if the C toolchain enabled
-Werror/-Wextra/-Wunused-parameter since it has unused parameters.

This change removes those flags when building the stdlib.

go/platform/apple.bzl

@@ -44,5 +44,7 @@ def apple_ensure_options(ctx, env, compiler_option_lists, linker_option_lists, t
     min_version = _apple_version_min(ctx, platform, platform_type)
     for compiler_options in compiler_option_lists:
         compiler_options.append(min_version)
+        # Allow unused parameters since they are present in the stdlib src.
+        compiler_options.append("-Wno-unused-parameter")
     for linker_options in linker_option_lists:
         linker_options.append(min_version)

go/private/context.bzl

@@ -100,6 +100,8 @@ _COMPILER_OPTIONS_DENYLIST = dict({
     # fmax-errors limits that and causes build failures.
     "-fmax-errors=": None,
     "-Wall": None,
+    "-Wunused-parameter": None,
+    "-Wextra": None,
 
     # Symbols are needed by Go, so keep them
     "-g0": None,